1. Leg 195 Summary1

Salisbury, M.H., Shinohara, M., Richter, C., et al., 2002 Proceedings of the Ocean Drilling Program, Initial Reports Volume 195

1. LEG 195 SUMMARY1

Shipboard Scientific Party2

INTRODUCTION

Ocean Drilling Program Leg 195 had three distinct objectives. The first segment of the leg was devoted to coring and setting a long-term geochemical observatory at the summit of South Chamorro Seamount (Site 1200), which is a serpentine mud volcano on the forearc of the Mariana subduction system (Fig. F1). The second segment was devoted F1. Location map showing sites to coring and casing a hole in the Philippine Sea abyssal seafloor (Site drilled during Leg 195, p. 33.

30° 1201) and the installation of broadband seismometers for a long-term N

Keelung 1202 subseafloor borehole observatory. During the third segment, an array of 25° Altitude/ Depth (m) 4000 advanced piston corer/extended core barrel holes was cored at Site 1202 20° 2000 1201 0

2000 under the Kuroshio Current in the Okinawa Trough off the island of ° 15 1200 4000 km Guam 6000 0 200 400 8000 Taiwan. ° 10 ° ° ° ° ° ° ° ° ° The drilling and observatory installation program at South 110 E 115 120 125 130 135 140 145 150 Chamorro Seamount was designed to (1) examine the processes of mass transport and geochemical cycling in the subduction zones and forearcs of nonaccretionary convergent margins; (2) ascertain the spatial variability of slab-related fluids in the forearc environment as a means of tracing dehydration, decarbonation, and water-rock reactions in subduction and suprasubduction zone environments; (3) study the metamorphic and tectonic history of nonaccretionary forearc regions; (4) investigate the physical properties of the subduction zone as controls over dehydration reactions and seismicity; and (5) investigate biological activity associated with subduction zone material from great depth. The seismic observatory in the Philippine Sea is an important component of the International Ocean Network seismometer net. By filling a large gap in the global seismic station grid, the observatory will help 1Examples of how to reference the increase the resolution of global tomographic studies, which have revo- whole or part of this volume. lutionized our understanding of mantle dynamics and structure. More- 2 Shipboard Scientific Party over, the observatory will allow more precise study of the seismic struc- addresses. ture of the crust and upper mantle of the Philippine plate, as well as Ms 195IR-101 SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 2 better resolution of earthquake locations and mechanisms in the northwest Pacific subduction zone. Drilling at Site 1201 was also designed to provide more precise basement age constraints for models of backarc spreading in the Philippine Sea as well as high-quality sediment sections that could be used to reconstruct the history of microplate motion, climate change, eolian transport, and arc volcanism in the region. Drilling at Site 1202 was designed to obtain a high-resolution sediment record under the Kuroshio Current to study global climate change, sea level fluctuation, local tectonic development, and terrestrial environmental changes in East Asia over the past 2 m.y. The Okinawa Trough is one of the few locations in the Pacific where the seafloor under the Kuroshio Current lies above the carbonate compensation depth, allowing the calcareous microfossil record to be preserved, and it is the only location with a high sedimentation rate, allowing high-resolution studies.

SITE 1200: SERPENTINE MUD VOLCANO GEOCHEMICAL OBSERVATORY

South Chamorro Seamount, Mariana Forearc

Geologic processes at convergent plate margins control geochemical cycling, seismicity, and deep biosphere activity within subduction zones. The study of input into a convergent plate margin by sampling the downgoing plate provides the geochemical reference necessary to learn what factors influence the production of suprasubduction zone crust and mantle in these environments. The study of the output in terms of magma and volatiles in volcanic arcs and backarc basin settings constrains processes at work deep in the subduction zone, but these studies are incomplete without an understanding of the through- put, the nature of geochemical cycling that takes place between the time the subducting plate enters the trench and the time it reaches the zone of magma genesis beneath the arc. Tectonically induced circulation of fluids at convergent margins is a critical element in the understanding of chemical transport and cycling within convergent plate margins and, ultimately, in understanding global mass balance (e.g., COSOD II, 1987; Langseth et al., 1988; Kulm and Suess, 1990; Langseth and Moore, 1990; Martin et al., 1991). In the shallow to intermediate suprasubduction zone region, dehydration reactions release pore fluids from bound volatiles in oceanic sediments and basalts of the downgoing plate (Fryer and Fryer, 1987; Peacock, 1987, 1990; Mottl, 1992; Liu et al., 1996). Fluid production and transport affect the thermal regime of the convergent margin, metamorphism in the suprasubduction zone region, diagenesis in forearc sediments, biological activity in the region, and, ultimately, the composition of arc and backarc magmas. Furthermore, these fluids, their metamorphic effects, and the temperature and pressure conditions in the contact region between the plates (the décollement) affect the physical properties of the subduction zone, where most major earthquakes occur. The discovery of Earth’s deep biosphere is recognized as one of the most outstanding breakthroughs in the biological sciences. The extent of this biosphere is currently unknown, but we are becoming increasingly aware that life has persisted in environments ranging from active hydrothermal systems on mid-ocean ridges to deep ocean sediments, SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 3 but so far no detailed investigations have been made of the potential for interaction of the deep biosphere with processes active in convergent plate margins. Determining unequivocally the composition of slab-derived fluids and their influences over the physical properties of the subduction zone, biological activity, or geochemical cycling in convergent margins requires direct sampling of the décollement region. To date, studies of décollement materials, mass fluxes, and geochemical interchanges have been based almost exclusively on data from drill cores taken in accretionary convergent margins (e.g., Kastner et al., 1993; Carson and West- brook, 1995; Maltman et al., 1997). Large wedges of accreted sediment bury the underlying crystalline basement, making it inaccessible to drilling, and the wedges interact with slab-derived fluids, altering the original slab signal. The dehydration reactions and metamorphic interchanges in intermediate and deeper parts of the décollements have not been studied in these margins. By contrast, nonaccretionary convergent margins permit direct access to the crystalline basement and produce a more pristine slab-fluid signature for two reasons: the fluids do not suf- fer interaction with a thick accretionary sediment wedge, and they pass through fault zones that have already experienced water-rock interactions, thus minimizing interaction with subsequently escaping fluids. Regardless of the type of margin studied, the deeper décollement region is directly inaccessible with current or even foreseeable ocean drilling technologies. A locality is needed where some natural process brings materials from great depths directly to the surface. The Mariana convergent margin provides precisely the sort of environment needed.

Geologic Setting

The Mariana convergent plate margin system is nonaccretionary, and the forearc between the trench and the arc is pervasively faulted. It con- F2. Bathymetric map of the south- tains numerous large (30 km diameter and 2 km high) mud volcanoes ern Mariana forearc, p. 34.

(Fryer and Fryer, 1987; Fryer, 1992, 1996) (Fig. F2). The mud volcanoes 144°E 146° 148° ° 20 Conical Seamount N

0 0 0 00 are composed principally of unconsolidated flows of serpentine mud 4 0 2 Pacman Seamount

0 0 0 4000 4 2 0 with clasts consisting predominantly of serpentinized mantle peridotite 0 0

Pagan Big Blue Seamount (Fryer, Pearce, Stokking, et al., 1990). Some have also brought up blue- 18°

4000 4 0 0 2000 schist materials (Maekawa et al., 1995; Fryer and Todd, 1999). Faulting 0 8000 Turquoise Seamount

4000 of the forearc to great depth produces fault gouge that when mixed 0 Celestial Seamount 00 00 0 2 2 16° Peacock Seamount with slab-derived fluids generates a thick gravitationally unstable slurry 6000 Blue Moon Seamount

4 of mud and rock that rises in conduits along the fault plane to the sea- 000 Saipan 2 0 0 0 0 0 0 floor (Fig. F3) (Fryer, 1992, 1996). These mud volcanoes are our most di- 4 ° 14 North Chamorro Seamount Guam rect route to the décollement and, episodically, through protrusion 8000

0 6000 0 0 0 00 2 6 events, open a window that provides a view of processes and conditions 4000 8 000 South Chamorro Seamount

6000 at depths as deep as 35 km beneath the forearc. 12° Prior to Leg 195, only one other active serpentine mud volcano 100 km (Conical Seamount) (see Fig. F2) had ever been sampled by drilling (Fryer, Pearce, Stokking, et al., 1990). Little was then known of either F3. Schematic cross section the processes that formed such seamounts, their distribution, and their through the Mariana system, relation to the tectonics of the forearc region or of the potential for un- p. 35. derstanding the deeper forearc processes they reflect. Recent advances Distance from trench axis (km) 100 50 0 0 in the understanding of the structure and tectonic evolution of non- Pacific plate Seamount Forearc sediment

Horst block Horst block accretionary forearcs, the nature of geochemical cycling within them, m, is rph Graben mo eta e m 10 ad -gr n, unt te tio amo dia ac , and the various active thermal, hydrologic, metamorphic, and biologi- se e mp on m i ed ter co at ns ct in sic tio u to s c d - de rea b ow tic u L ne S ge Depth (km) cal processes involved in the formation of mud volcanoes permitted the dia Legend Dip-slip motion

, Horizontal motion toward m 20 his Horizontal motion away orp planning of comprehensive studies of the intermediate-depth processes nt m , Serpentine mud volcano e ta n m e tio lle t m na co is o n Direction of subduction é ch rb tio Conduit of mud volcano D s ca dra s e de y n Blu eh tio d ac occurring within the “subduction factory.” By revisiting descriptions of re Pods of blueschist SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 4 serpentine melanges and “sedimentary” serpentinite terranes from past literature (Lockwood, 1972), we now realize that serpentine mud volcanism in convergent margin settings is not merely a local curiosity of the Mariana system but occurs worldwide. Site 1200 is located on a 200-m-high summit knoll on South Chamorro Seamount at 13°47′N, 146°00′E in a water depth of 2910 m, ~125 km east of Guam in the western Pacific Ocean. It lies 85 km from the trench, where the depth to the downgoing slab is ~26.5 km, based on studies by Isacks and Barazangi (1977). Pore fluids collected in gravity cores from this seamount exhibit a strong slab signal. It is the only known site of active blueschist mud volcanism in the world and sup- ports the only documented megafaunal assemblages associated with serpentine/blueschist mud volcanism (Fryer and Mottl, 1997). Side-scan surveys of this seamount (Fig. F4) show that the southeast- F4. HMR-1 side-scan imagery of ern sector of the edifice has collapsed, and debris flows of serpentine South Chamorro Seamount, p. 36.

145°45´E 146°00´ 146°15´ 146°30´ material (dredged in 1981 and observed during Shinkai 6500 dives in 14°50´ N

1995) blanket the inner slope of the trench from the summit of the sea- Fault block North Chamorro mount to the trench axis. The summit knoll sits at the apex of the sec- Seamount 14°00´ 0 00 4000 4 tor collapse, and its formation was most likely initiated in response to South Chamorro Summit knoll Seamount A 4000 B'

00 60 the collapse. Submersible observations show that the knoll’s surface is 5000

000 ° 4 0 13 45´ B Site A' 0 0 broken into uplifted slabs of cohesive serpentine mud (Fryer, 1996) sep- 1200 Debris flows 7

0 arated by meter-deep fissures with crosscutting orientations. Medium 8

13°30´

0 0 blue-green to dark blue serpentine mud and clasts of metamorphosed 0 8

7000 rocks are exposed. Low-temperature springs in the fissures support a 5000 7000 0 8000 8000 900

13°15´ vigorous biological community of mussels, gastropods, worm tubes, 6000 0 700 and galatheid crabs (Fryer and Mottl, 1997). The mussels are likely of Fault scarps 9000

Fault the genus Bathymodiolus, one which contains methylotrophic sym- block 13°00´ 0 50 bionts in its gills and requires high ambient concentrations of methane km in its feeding source (Fryer and Mottl, 1997). The pore fluid composition profiles and the presence of a vigorous biological community at the surface suggest that the summit knoll is a currently active seep region. The interior of the seamount shows little structure on six-channel seismic reflection profiles (Fryer and Mottl, 1997) (Fig. F5). This sea- F5. Multichannel seismic reflec- mount is likely an active serpentine mud volcano similar to Conical tion profiles over South Chamorro Seamount, drilled during Leg 125 (Sites 778–780), and thus provides an Seamount, p. 37.

Site 1200 (location is 2 km SW of this point) excellent drill target for studies of the active processes of these mud vol- AA' NW SE 4 canoes. It has the strongest slab signature in pore fluids from among 5 6

7 the seamounts sampled in 1997 and is comparable to Conical Sea- 8 Two-way traveltime (s) traveltime Two-way 9 Site 1200 mount in the strength of its slab signal. B (location is 3.5 km SE of this point) B' SW NE 4

7 Scientific Objectives (s) traveltime Two-way 8 010

km The overall objectives of drilling at South Chamorro Seamount were to (1) study geochemical cycling and mass transport in the subduction zones and forearcs of nonaccretionary convergent margins; (2) determine the spatial variability of slab-related fluids within the forearc environment as a means of tracing dehydration, decarbonation, and water- rock reactions both in the subduction zone and the overlying suprasubduction zone environments; (3) study the metamorphic and tectonic history of nonaccretionary forearc regions; (4) investigate the physical properties of the subduction zone and their influence on dehydration reactions and seismicity; and (5) investigate biological activity associated with subduction zone material from great depth. To achieve these scientific objectives, operations during Leg 195 were designed to recover sufficient materials to permit petrologic and miner- alogic characterization of the serpentine mud flow units, to analyze SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 5 their pore fluid compositions, to collect any biological material con- tained in the muds, and to deploy a long-term geochemical observatory at South Chamorro Seamount.

Establishment of a Seafloor Geochemical Observatory

The primary objective at South Chamorro Seamount was to deploy a long-term geochemical observatory in a cased reentry hole in the central conduit of the serpentine mud volcano. The reentry hole for the installation of a downhole thermistor string, pressure sensor, and osmotic fluid samplers was designed to be sealed with a circulation obviation retrofit kit (CORK). The techniques that were used to install the CORK were similar to those used for successful installations during Legs 139, 164, 168, and 174B (Davis et al., 1992). The hole at Site 1200 was CORKed with a thermistor cable to obtain a long-term record of the temperature variations in the sealed hole as the natural hydrologic system reestablishes itself after drilling. This installation will provide a long-term record of (1) the rebound of temperatures toward formation conditions after the emplacement of the seal; (2) possible temporal variations in temperature and pressure due to lateral flow in discrete zones, regional and/or local seismicity, and short-term pressure effects; and (3) the composition of deep circulating fluids obtained with the osmotic samplers. Data from the downhole instruments will be collected during an NSF-funded Jason/DSL 120 cruise that is tentatively scheduled to be conducted 18 months after Leg 195.

Fluid Transport

The drill site on South Chamorro Seamount was designed to help assess the variability of fluid transport and composition within the forearc. Previous field studies indicate that most of the fluid flow in the Mariana forearc is channeled along forearc faults and fault-controlled conduits in mud volcanoes. The pore fluid compositions are expected to vary depending on the nature of the channeling structures (diffuse network of small faults, major faults, and mud volcano conduits). In particular, fluids ascending through mud volcano conduits along well- established paths in contact with previously metamorphosed wall rock should carry the most pristine slab signature. This was certainly the case at Conical Seamount, drilled during Leg 125. The summit Site 780 produced by far the purest deep slab-derived fluids, based on their much lower chlorinity and higher K, Rb, B, H2S, and sulfate, whereas the flank Sites 778 and 779 produced combinations of slab-derived fluid and seawater that had reacted with peridotite and basalt at shallower crustal levels (Mottl, 1992).

Fluid Budgets

Although total fluid budgets are difficult to ascertain in any convergent margin, they are likely to be more readily determined at nonaccretionary active margins because the hydrologic flow systems operate on longer timescales than do those at accretionary margins. Attempts to determine the total fluid budgets at accretionary active margins have been hindered by the presence of lateral heterogeneity and transient flow processes. Lateral heterogeneity results in different flow rates and compositions along the strike of the margin. Transient flow apparently SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 6 results largely from the valvelike influence of the accretionary complexes themselves. Sediment properties vary with fluid pressure, and fluid pressure var- ies as a function of fluid production rate and transient hydrologic properties. Thus, the accretionary system acts as both a seal and a relief valve on the fluid flow system. The absence of such a short timescale, fluid pressure, and formation-properties modulator at nonaccretionary systems should allow fluids to escape more steadily. To test this hypothesis, the physical nature of fluid flow at nonaccretionary settings must be determined. Then fluid budgets can be constructed to determine whether the expected long-term flow is consistent with observations or if the flow must occur in transient pulses. The CORK experiment planned for the South Chamorro Seamount site will address this problem.

Along-Strike Variability

The composition of slab-derived fluids and deep-derived rock materials may differ along the strike of the forearc, reflecting regional variations in composition within the slab and suprasubduction zone lithosphere. The pore fluids from several of the forearc mud volcanoes already sampled are chemically distinct, and it was anticipated that the pore waters from South Chamorro Seamount would also be chemically distinct. These differences are probably associated not only with the depth to the slab but also with the physical conditions under which water-rock reactions occur and the variations in the regional composition of the plate and overriding forearc wedge. The geochemistry of the fluids from Conical Seamount is described in detail in several publications (Fryer et al., 1990; Haggerty, 1991; Hag- gerty and Chaudhuri, 1992; Haggerty and Fisher, 1992; Mottl, 1992; Mottl and Alt, 1992). These papers show the origin of the Conical Seamount fluids to be from dehydration of oceanic crustal basalt and sediment at the top of the subducting lithospheric slab. The compositions of the fluids from the PACMANUS hydrothermal field and seamounts farther south are reported in Fryer et al. (1999). Pore fluids from these indicate a slab source, as shown by their lower chlorinity and higher K and Rb, similar to that observed at Conical Seamount by Mottl (1992).

Pressure and Temperature Indicators from Fluids

The composition of slab-derived and deep-derived metamorphosed rock is useful in defining geochemical processes and estimates of the thermal and pressure regime at depth, and thus, for determining the physical properties of the décollement region. It was hoped that it would also be possible to constrain some of the pressure and temperature conditions under which certain dehydration reactions take place in the subducted slab. Pore fluids from Ocean Drilling Program (ODP) Site 780 at the summit of Conical Seamount are unusual because of geochemical and physical processes at depth. The observed enrich- ments in alkali elements and B in fluids from Site 780 are unambiguous indicators of a source temperature in excess of 150°C, yet the fact that these elements are depleted at Sites 778 and 779 on the flanks of Conical Seamount, relative to their concentrations in seawater, indicates that the deep slab signal can be readily overprinted by local peridotite-seawater reactions at lower temperatures. Not all chemical spe- SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 7 cies are affected by this overprinting, however (i.e., sulfur isotopic composition of dissolved sulfate) (Mottl and Alt, 1992). Thus, to avoid potential reactions between sediment and slab-derived fluids, we planned to collect fluids from mud volcano conduits, where continued focused flow provides a pathway for slab-derived “basement” fluids to reach the seafloor.

Metamorphic Parageneses

Studies of deep-derived minerals and metamorphic rock fragments brought to the surface in mud flows in serpentine seamounts can be used to constrain the pressure and temperature regimes under which the metamorphism that formed them took place. It is known, for in- stance, that the minimum pressures of formation for incipient blueschist materials from Conical Seamount are 6–7 kbar (Maekawa et al., 1995). Similarly, from the paragenesis of crossite schist recovered in cores from South Chamorro Seamount, it can be shown that pressures >7 kbar are consistent with their metamorphism. Examination of a more extensive collection of the muds and clasts from South Chamorro Seamount should make it possible to quantify the assemblages of muds and xenoliths present in the flows and constrain the ranges of pressure and temperature that exist in the source regions for these materials.

Biological Activity Associated with Deep-Derived Subduction Zone Material

Interest in the deep subsurface biosphere has grown dramatically as a result of recent studies linking extreme environments to the first living organisms that inhabited the Earth. The search for the last common an- cestor in the geologic record is moving toward high-temperature environments, such as those at spreading centers and hotspots both on the ocean floor and on land. Microbes and microbial products are abundant in oceanic hydrothermal environments and are presumed to be representative of a community of thermophilic and hyperthermophilic organisms that originated beneath the seafloor (Fisk et al., 1998). Mi- crobes are also involved in the transformation of minerals in the oceanic crust and in the cycling of elements in the crust; however, the origin of these microbes is much more controversial. Drilling at Chamorro Seamount provides a unique opportunity to determine the nature of microbiological activity in a very different kind of extreme environment, the high-pH, low-temperature environment associated with serpentine/blueschist mud volcanism (Fryer and Mottl, 1997; Fryer et al., 1999), and to reexamine the hypothesis that microbes are capable of using alternative energy sources that would support a heterotrophic subsurface ecosystem. In addition, because the pore fluids are more pristine in nonaccretionary convergent margins, it should be easier to assess from the chemistry of both the muds and the fluids whether organic syntheses capable of supporting life are active in these settings. Understanding the origin of the deep biosphere is a fundamental ODP objective and will further address the compelling question of whether life arose in extreme environments rather than on the surface of the early Earth. Although several experimental studies indicate that a thermophilic origin of life is possible, definitive proof must await an as- sessment of the full range of conditions in which life exists and the nature of life in these environments. SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 8

Mechanics and Rheology

The mechanics and rheology of serpentine muds in the Mariana forearc seamounts control the processes that formed the seamounts and their morphology. It was thus planned to conduct a rheological study of the serpentine muds to place realistic constraints on the mechanisms governing the ascent of the muds to the surface, the maintenance of the conduits, and the construction of the seamounts. Shipboard torsion-vane testing during Leg 125 at Conical Seamount in the Mariana forearc and at Torishima Forearc Seamount in the Bonin forearc showed that the serpentine muds are plastic solids with a rheology that bears many similarities to the idealized Cam clay model and is well described by critical-state soil mechanics (Phipps and Ballotti, 1992). These muds are thus orders of magnitude weaker than salt and are, in fact, comparable in strength to common deep-sea pelagic clays. The rate at which the muds rise relative to the fluids will likely influence the water-rock reactions and the character of the slab signal in fluids from these mud volcanoes. Better constraints on the nature of the fluids will permit a more accurate determination of the physical conditions of the décollement, where the fluids originate.

Drilling Strategy and Operations

After steaming to the site and lowering the pipe to the summit of the seamount, we planned to conduct a brief seafloor television survey of the conduit to locate the springs and mussel beds identified in Shinkai 6500 dives and to identify sites near the springs for rotary core barrel (RCB) coring and logging and relatively clast-free sites for advanced piston corer/extended core barrel (APC/XCB) coring, jet-in tests, and the establishment of a reentry hole. After conducting a jet-in test to establish the depth of the first casing string for the reentry hole, we planned to core and log an RCB pilot hole to 450 meters below seafloor (mbsf) to determine the nature of the formation and the ease of drilling on the seamount, a major concern because drilling during Leg 125 at Conical Seamount had been plagued with drilling problems. Depending on the results of the RCB hole, we then planned to offset and jet in a reentry cone and 20-in casing to ~25 mbsf and then drill a hole in stages to 420 mbsf for the CORK installation. In anticipation of hole instability problems, an elaborate casing program was envisioned, with cemented 16-in casing to 200 mbsf followed by 10.75-in casing to 400 mbsf, including 23 m of screened casing and a casing shoe at the bottom to prevent the serpentine mud from slowly invading the instal- F6. Location of Holes 1200A– lation from below. After the hole was drilled and cased, the instrumen- 1200E on the summit knoll of tation installed, and the remotely operated vehicle (ROV) platform em- South Chamorro Seamount, p. 38. placed, we planned to drill an APC/XCB hole to 420 mbsf to collect a 13°47.2´ N continuous, undisturbed section for petrologic and pore water studies. 2980 2 9 7 0 5 4 By drilling the APC/XCB hole last, the time allocated for APC/XCB cor- C D

° F 6 ing could be held in reserve as contingency time if it took longer than 13 47.0´ A 2 EB1,3 0 6 9 anticipated to drill the reentry hole and install the observatory. Not sur- 2

2970

2990 0 3 98 prisingly, the actual operations at Site 1200 unfolded rather differently. 0 2 0 0 90 29 00 The JOIDES Resolution arrived at Site 1200 (proposed Site MAF-4B) at 30 13°46.8´ 146°0.0´E 146°0.2´ 146°0.4´ 2100 hr on 11 March 2001. Following a 4-hr camera survey, Hole 1200A 0 0.2 km was spudded adjacent to a vent mussel community at the top of South Chamorro Seamount at 2200 hr on 11 March with the RCB and cored to a depth of 147.2 mbsf (Fig. F6; Table T1). High torque and lost rota- T1. Leg 195 coring summary, tion at this depth resulted in a stuck drill string that ultimately forced p. 63. SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 9 us to abandon the hole. Recovery in Hole 1200A was poor (147.2 m cored; 9.4% recovered), with little recovery of the mud matrix material surrounding the hard ultramafic clasts. The drill string was pulled out of the hole, and the seafloor was cleared at 1535 hr, ending Hole 1200A. The ship was then offset 25 m to the east, and Hole 1200B was spudded at 1640 hr on 13 March. Our intention was to wash to 147.2 mbsf and then start coring to the target depth of 450 m. By 1615 hr on 14 March, the hole had been advanced to a depth of 98.0 mbsf. Once again, high torque and overpull began to plague the hole. Despite consistent mud sweeps and multiple reaming attempts, the hole could not be stabilized. At 0645 hr on 14 March, we decided to abandon further drilling/coring efforts in the pilot hole and to start the reentry hole because it was obvious that deep penetration could not be achieved without the use of casing. Once the drill string was pulled out of the hole with the top drive, the ship was offset to the north and Hole 1200C was spudded at 0450 hr with the 20-in casing attached to the reentry cone. After a total of 18.25 hr of drilling with an 18.5-in bit, 22-in underreamer, and drilling motor, the reentry cone base reached the seabed, placing the 20-in casing shoe at 23.7 mbsf. Drilling of the 22-in hole for the 16-in intermediate casing string, without the motor this time, advanced smoothly and without incident. At 0130 hr on 18 March, the hole reached a depth of 140 mbsf. While we washed/lowered the casing string into the hole, however, the casing shoe encountered an obstruction 6 m off bottom that prevented the casing hanger from landing. After three futile hours, the drill string was recovered and one joint of casing was removed from the string. The shortened string was run back into the hole and washed F7. Casing configuration for the down without incident. With the 16-in casing shoe placed at a depth of geochemical observatory, p. 39.

107.4 mbsf, the casing string was cemented in place. The drilling pro- Top of reentry cone cess was then reinitiated using a 14.75-in drill bit and 20-in under- 2940.6 m reamer, dressed with 20-in cutter arms, and advanced to a depth of Seafloor depth 2943.0 mbrf 266.0 mbsf. The penetration rate deteriorated to zero at that point, and 20-in casing shoe a subsequent wiper trip found 9 m of soft fill at the bottom of the hole 23.7 mbsf 16-in casing shoe that was easily removed by circulation. Upon reaching the rig floor, the 107.4 mbsf underreamer was missing two out of three cutters. Because the hole had Top of 10.75-in penetrated below the base of the summit knoll but could not be deep- Perforated and screened casing screened casing 148.8 mbsf 53.5 m Bottom of 10.75-in ened further, the 10.75-in casing was deployed, reaching a depth of 10.75-in casing shoe screened casing (flapper sealed with Baker-loc) 202.3 mbsf 202.8 mbsf 224.0 mbsf by 0300 hr on 24 March without incident. However, Open hole

9 m of fill in progress beyond this point was not possible, and the string was pulled bottom of hole Total depth of hole out of the hole to remove three joints of casing. The shortened casing 266.0 mbsf string finally placed the shoe at 202.8 mbsf, with the screened interval extending from 202.3 to 148.8 mbsf (Fig. F7). F8. CORK configuration in Hole The CORK assembly, with two stands of 5.5-in drill pipe used as the 1200C, p. 40. stinger, was run in the hole, and the drill string was lowered to 53.0

Data mbsf. This left the CORK shy of landing out by ~8 m. At 1300 hr on 25 logger Reentry cone Depth (mbsf) March, the thermistor/osmotic sampler assembly was slowly run in the 0.0 Seafloor 0.3 Stinger 23.7 6 joints 20-in casing hole, and at 1430 hr the data logger was landed in the CORK body. Af- 5.5 in K-55, buttress 94 lb/ft 29.0 Stinger T10 58.0 reentry Cement 64.0 sub T9 ter 1 hr of pressure transducer calibration, the data logger was latched 15.8 lb/gal Thermistor cable 87.0 T8 107.4 16-in casing 110.0 Spectra line T7 K-55, buttress and the CORK body was then lowered the final few meters and latched T6 75 lb/ft 115.0 120.0 T5 125.0 T4 in place as in Figure F8. The CORK installations at Hole 1200C ended 130.0 T3 132.0 T2 with a successful free-fall deployment of the ROV platform. The pipe Extension cable 137.0 Osmotic was then returned to the surface; not counting the pilot holes, nine sampler 2 142.0 142.5 10.75-in casing Osmotic K-55, buttress round pipe trips totaling 52 pipe-km of tripping pipe were required to 147.5 sampler 1 40.5 lb/ft 149.0 Weak point

Osmotic Spectra line sampler 1 171.0 deploy the observatory. intake 174.0 Sinker bar After the successful installation of the geochemical observatory, the 176.0 202.3 10.75-in screen, K-55, buttress, 40.5 lb/ft 312.5-in holes/ft wrapped with 0.090-in diameter vessel was offset 40 m to the south and Hole 1200D was spudded with wire with 0.008-in gap over 266.0 0.125-in standoff rods SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 10 the APC to sample the serpentine muds for petrology, pore water, and microbiology studies at 1415 hr on 26 March. Coring continued to a depth of 44.4 mbsf using the APC advance-by-recovery method. Hard clasts were drilled with an XCB center bit assembly. After coring was halted by a hard clast at 44.4 mbsf, the XCB was used to deepen the hole. After advancing 9.0 m, however, the penetration rate fell to zero and the decision was made to abandon Hole 1200D. The vessel was then offset back to the location of the earlier identified mussel beds, and Hole 1200E was spudded with the APC for further pore water studies. Coring with the APC/XCB continued, again using the advance-by-recovery method for the APC cores, to a depth of 50.4 mbsf, where the scientific objectives of the hole were met. The ship was then offset 20 m to the north, and Hole 1200F was spudded at 1315 hr. Coring proceeded until the time allocated for operations at Site 1200 ran out. The hole depth reached 16.3 mbsf, with the recovery of APC Cores 195-1200F-1H through 3H. At 0200 hr on 29 March 2001, the ship was under way to the Guam pilot station.

Principal Results

The principal objective at Site 1200 was to install a borehole geochemical observatory at the summit of South Chamorro Seamount to sample fluids from the décollement below the Mariana forearc. Al- though this objective was achieved, no data will be recovered from the observatory until it is revisited by an ROV in 2003. As was to be expected in such an exotic environment, however, the drilling and coring undertaken to install the observatory and document its setting produced unexpected and often spectacular results. Perhaps the most fundamental achievement at Site 1200 was the documentation of the muds, xenoliths, and fluids rising to the surface from the mantle and the décollement zone through the central conduit of the mud volcano. The recovery in all cored holes consisted of poorly sorted, dark blue-gray to black serpentine mud breccia (Fig. F9) in F9. Serpentine mud breccia from which the muds are composed predominantly of silty clay–sized ser- South Chamorro Seamount, p. 41. pentine, and the clasts, which range up to a meter across, consist cm largely of serpentinized ultramafics. 85 Well-preserved and diversified subtropical assemblages of planktonic foraminifers and calcareous nannofossils were found in the top 0.1–0.3 90 m of the holes that were APC cored (Holes 1200D, 1200E, and 1200F), 95 indicating that the surface of the summit is blanketed with a veneer of calcareous microfossil-bearing deposits. A few species of benthic fora- 100 minifers are also present in small quantities in all holes. Samples far- thest away from the vent communities contain more abundant, diversi- 105 fied, and better-preserved microfossil fauna. The downcore sections in these three holes are virtually barren of microfossils, except for a pecu- 110 liar interval with folded color bands between 11 and 13 mbsf in Hole 1200D, which is interpreted as a paleosurface that has been covered or folded into the mud by the flow of serpentine. This interval contains abundant and diversified calcareous microfossils comparable to the core tops. The major difference is that these fossils tend to be robust species overgrown by calcite on the original structures, whereas the more delicate species have been dissolved. All the fossils are late Quater- nary in age. With the exception of the two calcareous intervals noted above, which are light yellow-brown to pink due to their microfossil content, and a 10- to 20-m-thick zone of strongly reduced, black serpentine SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 11 muds starting about a meter below the seafloor, the mud breccia in the conduit displays no stratigraphy, which is consistent with its mud volcano origin. It has been divided into two facies, however, on the basis of the abundance of clasts (<10% and 10%–30%); based on recovery, the average is ~7%. The smaller ultramafic clasts tend to be angular with planar external surfaces along early serpentine veins, whereas the larger clasts are subrounded to rounded, suggesting comminution by collisions during ascent. The mineralogy and composition of the muds and clasts almost all attest to a deep origin along the décollement zone or the overlying mantle, regardless of the particle or clast size, from silty clay to boulder. With the exception of aragonite produced at the mudline, where rising pore fluids interact with seawater to produce carbonates and rare zeolites (analcime) found farther down in the section, X-ray diffraction (XRD) analysis shows that the muds are dominated by serpentine minerals formed by the hydration of ultramafics + accessory glaucophane, spinel, garnet, chlorite, and talc derived from the metamorphism of mafic rocks along the décollement. Optical examination on board ship suggests lizardite/antigorite > chrysotile > brucite. The dual origin of the materials making up the mud breccia is even more clearly revealed in the grit fraction (0.1–1.5 cm). About 90% by volume of the grit fraction consists of partially to completely serpentinized ultramafic rocks, but 10% consists of metabasites, including glaucophane schist (Fig. F10), crossite/white-mica/chlorite schist, chlorite F10. Glaucophane schist in ser- schist (Fig. F11), white-mica schist, and amphibolite schist containing pentine mud, p. 42. blue-green to black amphibole and interstitial mica. These lithologies, especially the blueschists, are indicative of a high-pressure, low-temperature origin (Fryer et al., 1999; Fryer and Todd, 1999; Todd and Fryer, Gl 1999), and we interpret them as metamorphosed basic rocks from the descending slab. About 1% of the serpentine mud consists of blue sodic amphibole. Analysis of similar grains in gravity cores from South Chamorro Seamount showed a crossitic composition (Fryer et al., 0.25 mm 1999). The mineral grains are zoned with blue rims and lighter blue- green cores, implying relatively rapid ascent with the rising serpentine F11. Tremolite-rich chlorite schist muds. The rationale for this interpretation is that if the grains had been in serpentine mud, p. 43. in contact with rising fluids having the extreme compositions observed in the pore water analyses (see below) for geologically significant peri- ods of time, they would have likely back-reacted and would show retrograde metamorphic effects. Chl Although retrograde reactions are generally sluggish, the primary rea- son for this is the lack of reactive fluids in a system that has previously Tr experienced prograde regional metamorphism. Such metamorphism 0.5 mm drives volatiles out of the rocks, resulting in a dry system, which is far less likely to undergo retrograde metamorphism despite changes in pressure and temperature. The presence of highly reactive fluids in inti- mate contact with the serpentine muds at Site 1200, however, would make the possibility of retrograde reactions far more likely. None of the materials studied previously by Fryer and colleagues (Fryer et al., 1999; Todd and Fryer, 1999) have ever shown any indication of retrograde effects. The mineral grains from Site 1200 also lack retrograde effects. Although the grit fraction contains a rich and varied population of high P-T samples from the décollement, such samples appear to be absent from the large clasts, suggesting that the metabasites reaching the surface are preferentially smaller pieces. The abundance of phyllosili- cate minerals in the schists may contribute to the comminution of these samples as they rise from the source region. Pressure release as the SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 12 rock fragments rise may cause the phyllosilicates to expand and disinte- grate, and the continual collisions and mechanical grinding within the rising muds may cause the more friable rocks to break up into small fragments. As noted earlier, about 7% of the material recovered at Site 1200 consists of large clasts of partially to completely serpentinized ultramafic rocks from the mantle wedge under the Mariana forearc. Whereas serpentinization has been extensive in all samples (40%–100%; average = ~75%), there are sufficient relict minerals present in many of the samples to assess the original grain size (0.01–5.0 mm) and to determine that harzburgite is the dominant protolith, dunite is much less common, and lherzolite is rare. This is consistent with the whole-rock chemistry of the samples, which suggests that the ultramafics under- went 20%–25% melt extraction at some point during the formation of the arc (Fig. F12). The actual percentage of relict minerals is extremely F12. Composition diagrams for variable, with olivine ranging from 0% to 40%, orthopyroxene (ensta- Mariana forearc peridotites show- tite) from 0% to 35%, clinopyroxene from 0% to 5%, and chrome ing degrees of partial melting, spinel from 0% to 3%, depending on the original mineralogy and the p. 44. A 1 degree of serpentinization. In general, olivine and enstatite were the 30% melting

0.8 least stable minerals, with olivine altering readily to serpentine (lizard- Conical Seamount peridotites ite) or brucite + magnetite and enstatite altering to serpentine ± tremo- 0.6 (wt% rock) 3 0.4 O 2

lite/actinolite, whereas clinopyroxene and spinel were usually the most Al Torishima Seamount peridotites

0.2 South Chamorro resistant to alteration. Olivine often developed mesh and hourglass tex- Seamount peridotites 15% melting 0 tures during serpentinization, whereas enstatite is commonly replaced 0 0.5 1 1.5 2 2.5 CaO (wt% rock) B by bastitic textures. The serpentinization appears to have occurred in 90 30% melting Conical Seamount peridotites stages, because lizardite veins are often cut orthogonally by chrysotile 91 ) rock 2+ veins, producing spectacular “Frankenstein veins” consistent with uni- 92 + Fe

2+ form dilation during late-stage serpentinization along grain boundaries. /(Mg 93 2+ Torishima Seamount peridotites Mg × Interestingly, most of the ultramafics and all of the dunites show evi- South Chamorro 94 100 Seamount peridotites dence of deformation prior to serpentinization: the olivines commonly 15% melting 95 0 0.5 1 1.5 2 2.5 show kink banding and granulation and the enstatites (or their bastite CaO (wt% rock) replacements) often display undulatory extinction. The pore waters from Site 1200 revealed two distinct phenomena, a deep-sourced fluid that is believed to be upwelling from the top of the subducting slab 25–30 km below the seafloor and a new and exotic extremophile microbial community at 0–20 mbsf that is chemically ma- nipulating its environment. As can be seen in Figure F13, most pore wa- F13. Pore water composition vs. ter vs. composition profiles for the site represent nearly ideal advection- depth curves, p. 45.

A BCD E diffusion curves and the gradients in the top few meters are so steep 0 that they can only be maintained by upwelling from below. The deep 10 20 fluid is similar in many ways to that sampled at Conical Seamount to 30 40 Depth (mbsf) the north during Leg 125 (Fryer, Pearce, Stokking, et al., 1990). It has a 50 pH of 12.5 because it is in equilibrium with brucite, making it, along 60 70

80 with the Conical Seamount fluids, the most alkaline pore water ever 8 9 10 11 12 13 0 40 80 120 0.8 0.9 1 1.1 1.2 1.3 0 2000 4000 0 10 20 30 pH Alkalinity (mmol/kg) Na/Cl (mol/mol) Boron (µmol/kg) Sulfate (mmol/kg)

Hole 1200D Hole 1200E sampled in the deep sea. The pore water is also enriched in (mainly car- Hole 1200F Hole 1200A bonate) alkalinity (60 mmol/kg), Na (610 mmol/kg), Na/Cl (1.2), K (19 mmol/kg), B (3.2 mmol/kg), ammonia (0.22 mmol/kg), methane (2 mmol/kg), and C2 through C6 hydrocarbons, all components that are virtually absent in depleted harzburgites and therefore require a different source. The pore water is highly depleted in Mg, Ca, Sr, and Li and has low concentrations of Si, Mn, Fe, Ba, and phosphate. It is slightly depleted in chloride (510 mmol/kg in seawater) and enriched in sulfate (by 7% relative to chloride). This chloride depletion is much smaller than in the deep fluid from Conical Seamount, suggesting that the Conical conduit is more heavily serpentinized and less reactive, allowing more of the H2O from the deep source to arrive at the seafloor with- SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 13 out being lost to serpentinization along the way, or that the fluids are rising more rapidly at Conical Seamount and have had less time to re- act. Pore water composition vs. depth profiles also reveal that these deep fluids feed an active microbial community that is oxidizing light hydrocarbons from the fluid while reducing sulfate within the black serpentine mud in the upper 20 mbsf. This is a true extremophile community, operating at and probably driving the pH to 12.5, thus perpetuating its own ecosystem. Sulfate reduction is most active at two levels. Microbes within the upper level at 3 mbsf reduce seawater sulfate that diffuses downward against the ascending flow. Those within the lower level at 13 mbsf reduce sulfate that is supplied from the subducting slab by the upwelling fluid. As organic carbon is virtually absent within the depleted, serpentinized harzburgite, the microbes rely on methane and the C2 through C6 thermogenic hydrocarbons for their source of organic carbon and ammonia for their source of nitrogen. Both are supplied by the upwelling fluid. The microbial community intercepts these nutrients and effectively traps them within the ecosystem, where they can be recycled and continually enriched. This process explains the en- richment in organic carbon in the uppermost sediment. Iron sulfides and CaCO3 in the form of aragonite needles and chimneys are also enriched there by reaction between the ascending fluid, the microbial community, and the overlying seawater. As would be expected, the physical properties of the serpentine muds and clasts at Site 1200 are quite different and both are strongly influ- enced by the properties of serpentine. The velocities of the clasts, for example, range from 3.8 to 5.5 km/s and average 4.9 km/s, consistent with extensive serpentinization. Whereas the mud and the clasts have the same average grain density (2.64 g/cm3), the average bulk densities of the clasts and the muds are lower and quite different, 2.49 and 1.87 g/cm3, respectively. This is due primarily to differences in porosity between the clasts, which have low porosities, and the muds, which range from 40% to 60% porosity. Assuming the mud constitutes 93% of the breccia, the material in the conduit has an average density of 1.91 g/ cm3. If the average density of the crust is 2.75 g/cm3, then the buoyancy of the serpentine mud breccia in the upper crust would be ~0.8 g/cm3 before consolidation, or four times the density contrast between the salt in diapirs and most sedimentary rocks. Similarly, the buoyancy of completely consolidated serpentine mud breccia with a bulk density of 2.64 g/cm3 (the grain density) in fresh ultramafics (~3.2 g/cm3) would be ~0.5 g/cm3, or more than twice the buoyancy of salt in sedimentary rocks. Whereas the average shear strength of the serpentine mud (52.5 kPa) is high for sediments, it is orders of magnitude lower than that for rocks, which is consistent with their extrusion on the seafloor as mud volcanoes. Interestingly, although vent communities are observed on the summit, the borehole temperatures are very low in the upper 50 m in all of the holes measured at Site 1200, ranging from 2° to 3°C, or ~1.3°C above seafloor values. The heat flow values are quite variable, however, with those measured in Holes 1200A and 1200E near the springs aver- aging 15 mW/m2, considerably below the global average of 50 mW/m2, whereas the value measured in Hole 1200F, which was farther away, was ~100 mW/m2. The thermal conductivities of the muds are not unusual, ranging from 1.04 to 1.54 W/(m·K) with an average of ~1.32 W/(m·K), but the hydraulic conductivities are extremely low, ~0.6 cm/yr. SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 14

Unlike the physical properties discussed above, the magnetic properties of the clasts and muds are similar: the average natural remanent magnetization (NRM) intensities of both are high (0.49 and 0.44 A/m for the clasts and muds, respectively), as are their average susceptibili- ties (5.58 × 10–3 and 6.81 × 10–3, respectively). In both cases, the magnetization disappears at a Curie temperature of 585°C, indicating that the dominant magnetic mineral is magnetite produced by serpentinization. The only significant difference is that the NRM in the serpentine muds is unstable, whereas that in the clasts tends to be stable, with a high Koenigsberger ratio (average = 2.4). The NRM inclination and declination vary randomly with depth in single long pieces, however, indicating that the magnetization was acquired (i.e., serpentinization occurred) over a relatively long period or when the rock was being deformed or tumbled in the décollement or the conduit of the seamount.

SITE 1201: ION SEISMIC OBSERVATORY

West Philippine Basin

Tomographic studies using earthquake waves propagating through the Earth’s interior have revolutionized our understanding of mantle structure and dynamics. High-quality digital seismic data obtained from seismic stations on land, for example, have been used to identify zones of anomalous velocity and anisotropy in the mantle, and from these, to determine patterns of mantle flow. In particular, Tanimoto (1988) has demonstrated the existence of a strong pattern of deep (>550 km) high-velocity anomalies in the western Pacific, suggesting complex interaction between subducting slabs and the surrounding mantle, whereas more recent studies in areas of dense seismic coverage have provided crude images of subducting plates extending to the 670-km discontinuity (van der Hilst et al., 1991; Fukao et al., 1992) and of deep velocity anomalies extending beneath ridges (Zhang and Tanimoto, 1992; Su et al., 1992). One of the critical problems facing seismologists who wish to im- prove such tomographic models is the uneven global distribution of seismic stations. Few seismic stations are located on the 71% of the Earth’s surface covered by oceans, and this problem is particularly acute in large expanses of ocean such as the Pacific. The scientific importance of establishing long-term geophysical observatories at deep ocean sites to understand the dynamic processes occurring in the Earth’s interior through seismic imaging has long been recognized by the earth science and ocean drilling communities (COSOD II, 1987; JOI-ESF, 1987; Purdy F14. Location of seismic station and Dziewonski, 1988; JOI/USSAC, 1994; Montagner and Lancelot, coverage in the northwest Pacific 1995). The International Ocean Network (ION) project has identified region, p. 46. the western Pacific and the Philippine Sea as a particularly important gap in the global seismic network. By installing long-term borehole seis- 40° WP-2 N JT-1 INU mic observatories in the seafloor in this region, the ION project is at- TJN JT-2 tempting to fill this gap so that high-resolution tomographic images of ISG OGS MCSJ slab–mantle interaction zones can be obtained at great depth in the 20° most active system of subduction complexes in the world. To this end, BAG 1201 borehole seismic observatories were installed at ODP Sites 1150 and PATS 0° JAY

1151 (Stations JT-1 and JT-2 in Fig. F14) on the inner wall of the Japan km PMG 0 500 1000

Trench during Leg 186 (Suyehiro, Sacks, Acton, et al., 2000) and an- 100°E 120° 140° 160° 180°

ION seafloor borehole station other observatory was successfully installed at Site 1179 in the western Current OHP land station Past OHP land station IRIS land station SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 15

Pacific (Station WP-2 in Fig. F14) during ODP Leg 191 (Kanazawa, Sager, Escutia, et al., 2001). A major objective of the ION project was to establish a borehole seismic observatory at a quiet site in the middle of the Philippine Sea on the upper plate of the Mariana subduction system to determine whether the Pacific plate is penetrating into the lower mantle below the 670-km discontinuity under the Mariana Trench but not under the Izu- Ogasawara (Bonin) Trench. A high-quality digital seismic observatory was thus installed during Leg 195 at Site 1201 in the West Philippine Basin west of the Kyushu-Palau Ridge between existing stations at Inuyama (IMA) and Taejon (TJN) to the north, Minami Torishima (MCSJ) and Chichijima (OGS) to the east, Ponphei (PATS) and Jayapura (JAY) to the south, and Ishigakishima (ISG) and Baguio (BAG) to the west (Fig. F14). The observatory is designed as a stand-alone system with its own battery pack and recorder at the seafloor so that it can be serviced and interrogated by an ROV. Like the borehole observatories installed at Sites 1150 and 1151, however, there is a coaxial trans- oceanic telephone cable (TPC-2) near Site 1201 that can be used eventually for data recovery and power. There are plans to connect data, control, and power lines to the TPC-2 cable, which is owned by the University of Tokyo, after confirmation of data retrieval. This is done under the auspices of the Ocean Hemisphere Network Project, a national program from 1995 to 2001 in Japan. The data will eventually become accessible worldwide through the Internet.

Geologic Setting

Site 1201 is located in the West Philippine Basin in 5711 m of water ~100 km west of the inactive Kyushu-Palau Ridge and 450 km north of the extinct Central Basin Fault (Fig. F15). Early interpretations of mag- F15. Location map showing DSDP netic lineations (Hilde and Lee, 1984) indicated that the site lies on 49- and ODP sites in the Philippine Ma crust near Chron 21 and formed by northeast-southwest spreading Sea, p. 47.

25° on the Central Basin Fault. The spreading direction then changed to (57±1) N n a 22 24 iw 21 a T 16 17 23 294 17 20 north-south at ~45 Ma, and spreading finally ceased at ~35 Ma as volca- 18 295 24 18 22 (49±2) 19 19 19 21 23 18 16 19 20 21 14 22 ° 20 18 nism stopped on the Kyushu-Palau Ridge. Because the earliest magnetic 20 14 e 19 16 17 20 1201 g 13 16 21 id 17 14 18 21 R 22 17 19 447 u 14 16 19 la anomalies in the region predate the initiation of subduction at ~45 Ma 18 16 18 290 a 16 (43) 19 14 17 18 -P 17 16 16 17 19 u 14 h 19 18 17 16 18 s 20 18 u 14 14 17 y 16 16 K along the Kyushu-Palau Ridge, Hilde and Lee (1984) considered that the 19 17 14 14 ° 20 16 15 21 1413 18 17 16 20 18 17 19 18 Philippine Sea initially formed by entrapment of an older Pacific 21 20 19 19 anomaly 13 20 Altitude/ 35 14 21 West 15 Philippines Depth (m) 16 Philippine spreading ridge. More recent bathymetric and magnetic surveys (Okino 40 17 21 Sea 4000 10° 18 45 19 22 2000 20 23 21 0 50 24 et al., 1999) show that the site lies at the transition from well-defined 22 2000 23 25 55 24 26 4000 25 60 26 km 6000 Ma 8000 anomalies south of the Oki-Daito Ridge to more complicated anomalies 0200400 5° to the north, which implies that the crust to the north may have 120° E 125° 130° 135° 140° formed at a different spreading center. Analysis of paleolatitude and declination data from the Philippine plate and its margins suggests that the plate has drifted about 15° to the north and rotated clockwise by up to 90° since the middle Eocene (Hall et al., 1995). F16. Reflection line OT97 showing The sediment section at Site 1201 was predicted to be ~400 m thick the location of Site 1201, p. 48.

CDP number based on recent seismic reflection surveys showing a two-way travel- 600 700 800 900 1000 7 SW NE time to basement of 0.45 s (Fig. F16). Drilling at other sites in the re- Site 1201 gion during Deep Sea Drilling Project (DSDP) Legs 31 and 59 (Karig, In- gle, et al., 1975; Kroenke, Scott, et al., 1981) recovered a relatively barren deepwater section dominated by Holocene to Eocene– 8 Paleocene(?) brown pelagic clays overlying basement near the Oki- Daito Ridge (DSDP Sites 294 and 295). At DSDP Sites 290 and 447 to the (s) traveltime Two-way south, the section consists of a barren interval of Pliocene clays under- km

012 lain by Oligocene nannofossil-bearing silty clays mixed with ash. This 9 OT97 line 3 migrated SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 16 was underlain by a thick section of polymict and volcanic breccia presumably derived from the Kyushu-Palau Ridge to the east. The underlying basement consists of 80% basalt pillows and 20% diabase. Because Site 1201 lies in a similar setting at the foot of the Kyushu-Palau Ridge, it was considered likely that the section would be similar to that at Sites 290 and 447.

Scientific Objectives

The principal objective at Site 1201 was to install a long-term borehole seismic observatory in the middle of the Philippine plate to im- prove global seismic coverage, to study the structure of the upper mantle under the Philippine Sea, and to study plate interactions in the western Pacific. It was also expected that drilling at Site 1201 would provide samples representative of the Eocene/Paleocene crust of the northern West Philippine Basin. Results from this site would thus aug- ment those obtained during DSDP Legs 31 and 59, which were the first legs to sample and estimate the age of basement in the region and to confirm that the seafloor formed by backarc spreading. Results from this site will also add to our knowledge of backarc crustal structure and geochemistry, microplate tectonics, magnetic lineations, and sedimentation. Because core quality and dating techniques have vastly im- proved since these early legs, it was also anticipated that drilling at Site 1201 would provide better age control on backarc spreading as well as detailed records of Northern Hemisphere climate change, eolian transport, and arc volcanism in the region during the Tertiary.

Establishment of a Borehole Seismic Observatory

As outlined above, one of the main reasons for installing a borehole seismic observatory in the middle of the Philippine plate was to achieve homogeneous seismic coverage of the Earth’s surface with at least one station per 2000 km in the northwestern Pacific area (Fig. F14). Aside from plugging an important gap in the global seismic array, the Site 1201 observatory will produce high-quality seismic data. Tests with other borehole seismometers show that the noise level for oceanic borehole instruments is much lower than for most land stations (e.g., Stephen et al., 1999). High-quality seismic data from this site will be used for several purposes. Earthquake Mechanisms First, an observatory at Site 1201 will provide data from the backarc side of the Izu-Ogasawara and Mariana Trenches, giving greater accu- racy and resolution of earthquake locations and source mechanisms. The observatory will also be valuable for resolving events in the Ryukyu and Philippine Trenches because its location is analogous to that of station WP-2 off the Japan Trench. Structure of the Philippine Plate Observations of seismic surface waves as well as various phases of body waves from earthquakes along the margins of the Philippine plate will provide sufficient data to map differences in plate structure among the different basins comprising the plate (e.g., the West Philippine, Shikoku, Japan, and Parece Vela Basins). Only a few previous studies with limited resolution exist on the lithospheric structure of these areas (Seekins and Teng, 1977; Goodman and Bibee, 1991). Surface wave data SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 17 suggest that the plate is only ~30 km thick (Seekins and Teng, 1977). Such a value is inconsistent with predicted values from age vs. heat flow and age vs. depth curves (Louden, 1980). A long-line (500 km) seismic refraction experiment in the West Philippine Basin could not image the lithosphere/asthenosphere boundary (Goodman and Bibee, 1991). Mantle Structure and Dynamics Finally, Site 1201 will provide higher seismic resolution of mantle and lithosphere structures in key areas that are now poorly imaged. There are indications that the subducting Pacific plate does not penetrate below the 670-km discontinuity and that it extends horizontally (Fukao et al., 1992; Fukao, 1992), but the resolution of these studies is poor (>1000 km) beneath the Philippine Sea and the northwestern Pacific, especially in the upper mantle, where significant discontinuities and lateral heterogeneities exist (Fukao, 1992). Data from Site 1201 will be crucial in determining whether the Pacific plate is penetrating into the lower mantle in the Mariana Trench but not in the Izu-Ogasawara (Bonin) Trench (van der Hilst et al., 1991; Fukao et al., 1992; van der Hilst and Seno, 1993) and in determining how the stagnant slab eventually sinks into the lower mantle (Ringwood and Irifune, 1988). De- tailed images of mantle flow patterns may also help explain how backarc basins open and close and explain the mantle heterogeneity that causes the basalts sampled from western Pacific marginal basins to have Indian Ocean Ridge isotopic characteristics (Hickey-Vargas et al., 1995). In addition to the seismic objectives at Site 1201, we recognized that coring at the site might accomplish a number of important geologic objectives.

Age of Basement

Although the age of the basement in the northern West Philippine Sea has been estimated from magnetic anomalies, paleontologic confirmation has been imprecise because of spot coring, core disturbance, and poor preservation of microfossils. By continuous coring to basement using modern coring techniques, we hoped to obtain an accurate basement age from undisturbed microfossils, magnetostratigraphy, or radiometric dating of ash horizons. This information would be of considerable importance in constraining models of backarc spreading.

Basalt Chemistry and Crustal Thickness

Recent studies on the relationship between mid-ocean-ridge basalt (MORB) chemistry and crustal thickness indicate that the degree of partial melting is strongly controlled by the temperature of the upwelling mantle at the ridge. The volume of the melt (represented by the crustal thickness) and its chemical composition are sensitive to the temperature. This means that a knowledge of crustal thickness in an ocean basin makes it possible to estimate the temperature at which the crust was formed and the concentration of major and minor chemical elements in the resulting basalts (e.g., Klein and Langmuir, 1987; White and Hochella, 1992). To date, these studies have concentrated on young MORBs. The chemical model on which these predictions are based still has large uncertainties, partly because there are few cases off ridge where rock samples and high-quality seismic data have been collected at the same location. Chemical analysis of the basalt samples from Site SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 18

1201 should provide clues as to why the crust in the Philippine Basin is 3 to 4 km thinner than normal.

Tertiary Climate Record

Previous drilling in the West Philippine Sea was conducted during DSDP Legs 31 and 59 before the advent of piston coring, and many of the holes were only spot cored. As a consequence, the available core from the region is almost useless for stratigraphic and paleontologic reconstructions. By obtaining a continuous, high-quality record of pelagic sedimentation supplemented by high-quality logs, we hoped to obtain a proxy record of Tertiary climate change for the region. It was anticipated that the upper levels of the section might also contain a record of eolian transport from Eurasia.

Ash Fall Record

Although ash and tuff were present in the sediments recovered in the region during previous legs, it was impossible to reconstruct the ash fall stratigraphy because of core disturbance and the discontinuous nature of the coring. By continuous coring using APC and XCB techniques and correlation with high-resolution Formation MicroScanner (FMS), natural gamma spectrometry tool (NGT), and ultrasonic borehole imager (UBI) logs, we hoped to obtain a detailed record of arc volcanism around the Philippine Sea.

Philippine Plate Paleolatitude, Rotation, and Tectonic Drift

Paleomagnetic measurements of sediments and basalt cores are important because oriented samples are difficult to obtain from the oceans. The basalts record the direction of the magnetic field at the time the basalts were emplaced and can be used to infer the paleolatitude of the site (e.g., Cox and Gordon, 1984). Although it was unlikely that enough flow units would be cored at Site 1201 to average secular variation adequately, it was thought that the results would be useful in determining a Paleogene paleomagnetic pole for the Philippine plate. Sediments are typically a good recorder of the Earth’s magnetic field and should contain a continuous record of the movement of the Philip- pine plate through the Cenozoic. By collecting oriented sediment cores, we hoped to study the rotation of the Philippine plate and the initiation of subduction of the Pacific plate.

Drilling Strategy and Operations

After arriving on site, we planned to drill and core two pilot holes to determine the geology of the formation and to establish the casing re- quirements for the reentry hole that was to house the borehole seismic observatory. The first was to be APC cored to refusal (estimated at 200 mbsf) with the Tensor core orientation tool then XCB cored to basement, estimated at ~370 mbsf. After a jet-in test, a second pilot hole was to be drilled to basement and then cored 100 m into basement using the RCB to determine the nature of the basement. This hole would then be logged to identify a suitable interval for setting the seismometer package. Once the pilot holes had been completed, we planned to offset and jet in a reentry cone and ~60 m of 16-in casing. The hole would then be SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 19 reentered and deepened to ~425 mbsf with a 14.75-in tricone bit to lower a 410-m string of 10.75-in casing ~40 m into basement and cement it in place. The hole would then be reentered again and deepened to ~100 m in basement for the seismometers. After the seismometer package had been made up, lowered into the hole, and cemented in place, a battery package would be lowered into the throat of the reentry cone and acoustically released. The pipe would then be tripped to the surface, bringing the deployment to completion so that it could be activated by an ROV at a later time. As at Site 1200, however, the actual operations at Site 1201 departed significantly from those that had been planned. The JOIDES Resolution arrived on site at 1600 hr on 31 March 2001, following a 2-day transit from Guam. After the pipe was lowered to the seafloor, Hole 1201A was spudded with the APC/XCB to study the sediment section but the hole was abandoned after one core because of a premature APC shear pin failure. APC coring was then initiated in Hole 1201B at 1905 hr on 1 April and continued to a depth of 46.7 mbsf, after which the hole was deepened with the XCB to 90.3 mbsf (Table T1). The vessel was then offset 15 m to the west and a third APC hole, 1201C, was spudded and cored to refusal at 48.1 mbsf to provide a re- peat section through the soft sediments. The Tensor core orientation tool was used on the third, fourth, and fifth cores in both Holes 1201B and 1201C, and a temperature measurement was taken with the Adara shoe at a depth of 44.6 mbsf in Hole 1201C. A problem with the spooling of the coaxial cable used for the undersea television camera became apparent during the deepwater operations at the site. Since the undersea camera was required for reentry and the deployment of the seismic observatory, we decided to search for a deepwater pocket where we could fully extend and retension the cable in an attempt to correct the problem. After steaming 204 nmi northwest to a small basin indicated on Japanese hydrographic charts, we deployed the coaxial cable to a depth of 6183 m and fixed the spooling problems. At 0718 hr on 5 April, the vessel was back at Site 1201 and the main pilot hole, Hole 1201D, was spudded 120 m south of Hole 1201C. The hole was drilled with a center bit to a depth of 80.4 mbsf, where RCB coring was initiated. Coring proceeded without incident to basement at 510 mbsf, which was considerably deeper than initially predicted, and then continued another 90 m into the basement to a total depth of 600 mbsf. After releasing the bit, Hole 1201D was logged with the triple combination (triple combo) tool from 80 mbsf to total depth. A second logging run with the FMS-sonic tool could not pass an obstruction at 366 mbsf because of deteriorating hole conditions. After completing F17. Borehole seismometer instru- the run in what was left of the open hole, the pipe was lowered again in ment package, p. 49. an attempt to reopen the hole for logging but an impassable bridge was reached at a depth of 90 mbsf. At that point, a 50-m plug of cement was set to prevent future fluid communication with the cased reentry hole and seismometer. The hole for the seismometer was initiated at 1600 hr on April 14, OBH (T1023[D003]) when Hole 1201E was spudded with a reentry cone and 16-in casing and jetted in to a depth of 39.1 m. The hole was then drilled to 543.0 BIA mbsf and cased with 10.75-in casing to a depth of 527.0 mbsf, or 15 m into basement. After cementing the casing in basement, the 9.875-in OBH (T1038[D417]) ION installation hole was drilled to a total depth of 580 mbsf. By 1230 hr on 23 April, the seismometer instrument string was assembled and final electrical integrity checks were completed (Fig. F17). Hole 1201E was then reentered and the instrument package was lowered into the SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 20 hole without incident. The seismometer package was cemented in place F18. Configuration of reentry with the end of the stinger located at a depth of 568.7 mbsf (Fig. F18). cone, casing, and ION seismic ob- The top of the uppermost seismometer was placed ~558.4 mbsf, or servatory components, p. 50.

Top of riser/hanger (8.1 m) ~46.4 m below the basement contact. At 0830 hr on 24 April, the bat- J-tool to disconnect from drill string Casing hanger body Data control unit (MEG-195) tery platform was lowered through the moonpool and landed in the re- 4.5-in through casing ROV platform (5.05 m) Battery/recorder unit (PAT) Centralizing ring × 683-mm ID (top) 3200-mm diameter 2640-mm height (leg) 3658-mm diameter entry cone at 1400 hr (Fig. F19). A handheld acoustic command unit Centralizer

Top of reentry cone (2.41 m) was used to release the platform. Proper platform installation was con- Reentry cone Reentry cone base Seafloor firmed with the subsea television camera, and by 1100 hr on 25 April, (5721 mbsl) Pelagic silty clay Landing point (0.3 mbsf) the ship was secured for transit and under way to Site 1202 (alternate 16-in casing Bottom of 16-in casing (39.0 mbsf)

54.0 mbsf Centralizer Site KS-1). Turbidites 10.75-in casing

Circulating sub cement level in 4.5-in casing (278.4 mbsf)

Cement level in 10.75-in casing (384.4 mbsf) Bottom of 10.75-in casing (527.0 mbsf) Principal Results Bottom of 14.75-in rat hole (543.0 mbsf) 512.0 mbsf 9.875-in open hole Cement Basalt Bottom of 4.5-in casing (558.4 mbsf) Bottom of upper seismometer (561.2 mbsf) Bottom of lower seismometer (564.2 mbsf) Bottom of stinger (568.7 mbsf) The principal objective at Site 1201 was to install a long-term bore- Rat hole Bottom of 9.875-in hole (580.0 mbsf) hole seismic observatory in the middle of the Philippine plate. Al- though this was successfully accomplished, the observatory will not be activated until its brains are installed during an ROV visit in the spring F19. ROV landing platform, p. 51. of 2002 and no data will be recovered until it is revisited in 2002 or SAM frame 2003. In the meantime, the core recovered during the course of prepar- Top plate ing the hole for the observatory produced striking and, in some cases, (ROV platform) 3.200 m unexpected results. Drilling at Site 1201 yielded a composite 600-m-thick section consist- LBU 2 ing of 510 m of Miocene through late Eocene sediments and 90 m of UMC cable basalt. The sedimentary section consists of two lithostratigraphic units LBU 1 3.658 m

(Fig. F20). The uppermost unit (0–53 mbsf) consists of soft pelagic clays, .6

2 cherts, and interbedded sandstones and silty claystones that contain significant amounts of red clay. The underlying unit (53–510 mbsf) is composed of a thick section of interbedded turbidites composed of detrital volcaniclastic material and traces of reef detritus from the Kyushu- F20. Lithology, color, natural Palau Ridge, which range in size from coarse sandstones and breccia gamma count, and mineralogy vs. through silty claystone to claystone. The individual turbidite layers depth and age, p. 52.

Graphic lithology Lith. Color Natural range from tens of meters to a few millimeters in thickness and tend to log Age unit reflectance gamma radiation Mineralogy cssg 0 IA e. Plio. e. decrease in thickness and grain size downsection (Figs. F21, F22), re- 50 Oligo. to l. IB IC

100 flecting a gradual change from high-energy to low-energy deposition. IIA 150

The basal 20–30 m of the unit consists of interbedded turbidites and 200 reddish tan to chocolate-brown claystones deposited in a quiet marine 250 IIA 300 Depth (mbsf) 350 environment. One of the most striking features of the entire sediment late Oligocene to Eocene

400 section at Site 1201 is the color of the turbidites, which range from dark IIA 450

500 IIB gray to dark greenish gray in the upper 240 m of the unit, where the + + +

+ +

+ Illite 550 + + + Quartz Erionite + + Gypsum Pyroxene Phillipsite + Basaltic Chabazite basement + + Plagioclase volcaniclastics are (relatively) fresh, and then range from deep green to + 600 -10 0 1020 0 10 20 30 Analcime/Wairakite green red a* (cps) Heulandite/Clinoptilolite gray-green to the base of the unit. Thin section and XRD analyses show ExpandableWell-crystallized clay minerals smectite that these changes are related to progressive alteration with depth, including the devitrification of glass, the replacement of the calcic cores F21. Laboratory multisensor track of plagioclase by clays, and the infilling of voids and vesicles by clays measurements, p. 53. and zeolites in the upper part of the unit, and the wholesale replace- Graphic lithology Lith. log Age unit ABC cssg 0 ment of volcaniclastic material in the lower part of the unit by smectite, IA

IB to l. Oligo. to l. l. Pliocene l. chlorite, and zeolites (chabazite, erionite, heulandite/clinoptilolite, and IC 100 analcime/wairakite) during diagenesis. IIA

The composition of the interstitial water at Site 1201 is very unusual 200 for deep-sea sediments and reflects the profound diagenesis that has oc- IIA

300 late Oligocene curred in the turbidites in the lower part of the section. The most strik- to late Eocene Depth (mbsf) ing feature is an extremely large increase in pH, Ca, and chlorinity with 400 depth in the pore water; whereas seawater is mainly a sodium chloride IIA

solution, the altered seawater near the base of the sediments is mainly a 500 IIB + +

+ +

+ + Basaltic calcium chloride solution (Fig. F23). Calcium increases to 270 mmol/ basement +

+ + + 600 0 2000 1230102030 kg, 27 times the concentration in seawater, by leaching from the volca- Magnetic susceptibility Density NGR (× 10-5 SI) (g/cm3) (cps) SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 21 niclastic material. Similarly, chlorinity increases to 645 mmol/kg, 20% F22. Logging results from Hole higher than seawater values, due to the removal of water during the for- 1201D, p. 54.

Density PorosityResistivity Velocity Hole diameter core core shallow core Graphic mation of hydrous minerals such as clays and zeolites. The gain in Ca is 3 Ω lithology 020(in)(g/cm ) 0(%) 100 1( m) 200 1500(m/s) 3500 Gamma ray log log deep log log 3 Ω Core Recovery Depth (mbsf) Lith. unit Lith. 055(gAPI) 1(g/cm ) 3 0(%) 100 1( m) 200 1500(m/s) 3500 Logging unit cssg 0 balanced by the removal of 70% of the Na (to 140 mmol/kg) and the IA IB IC loss of nearly all of the Mg and K from the seawater during the forma- Pipe depth Pipe depth 1 1R 2R 100 3R a 4R IIA 5R 6R tion of clay, smectite, and zeolites. Sulfate decreases as well, from 28 to 7R 8R 9R 10R b 11R 12R 15 mmol/kg, by the precipitation of gypsum in response to the elevated 13R 200 14R 15R 16R 17R 18R c IIA Ca concentration. Alkalinity falls from the seawater value of 2.4 to <1 19R 20R 21R 22R 23R 300 * 24R 25R d meq/kg as it is consumed by the precipitation of authigenic minerals. 26R 27R 28R 29R 30R 31R * The rise in pH to 10.0 from the seawater value of 8.1 also reflects ex- 32R Splice depth 33R 34R 400 35R * 36R IIA 37R treme alteration. Many of the pore water gradients in the top of the tur- 38R 39R * 40R 41R 42R 43R 44R 500 bidite section can only be supported by ongoing reactions, which is 45R IIB 46R + + 47R + 2 + + 48R + 50R 49R + + 51R + 52R + + consistent with the fact that the volcaniclastics at this level are not yet Basaltic +

53R basement + + 54R + 55R completely altered. Deeper in the section, however, many of the 600 geochemical gradients approach zero, implying that equilibrium has been achieved and that the geochemistry observed is that of “fossil” F23. Pore water Mg, Ca, Na, and pore water. alkalinity concentrations vs. To reconstruct the geological history of the site and determine the depth, p. 55. timing of diagenesis, it is necessary to look at the microfossil and paleo- Graphic lithology log cssg ABCD 0 Age unit Lith. 0 magnetic record. The topmost (0–29 mbsf) and lowermost (462–509 IA IB to l. Oligo. to l. 50 Pliocene l. IC mbsf) sections are barren of nannofossils, but moderately to poorly pre- 100 100 IIA served nannofossils in the middle section allowed us to recognize six 150 200 200 biozones spanning Zones NP19/NP20 to NP25 (Fig. F24). The turbidites 250 IIA between 53 and 462 mbsf represent an expanded sequence of late Depth (mbsf) 300 300 350 Eocene to early Oligocene age. Separated by a short hiatus and lying on late Oligocene to Eocene 400 400 IIA 1201A 450 1201B top of the turbidites is a 25-m sequence of upper Oligocene (Zone 1201D

500 IIB 500 NP25) red claystone. Compared to DSDP drilling results at Sites 290 and 0 20 40 60 0 100 200 300 100 300 500 0 0.5 1 1.5 2 2.5 Magnesium Calcium Sodium Alkalinity (mmol/kg) (mmol/kg) (mmol/kg) (meq/kg) 447 (Karig, Ingle, et al., 1975; Kroenke, Scott, et al., 1981), the upper Eocene sediments (>34.3 Ma) recovered at this site are the oldest so far identified on the sedimentary apron of the Kyushu-Palau Ridge. Be- F24. Nannofossil ranges at Site cause the 47-m interval overlying basement at the site could not be 1201, p. 56. dated on board ship, this is clearly a minimum age; dating of this criti- Graphic lithology log cssg Zone Age (Ma) Lith. unit Lith. cal interval must await the results of shore-based radiolarian studies. 0 D. bisectus C. abisectus Z. bijugatus D. tanii ornatus B. serraculoides H. compacta S. pseudoradians S. predistentus S. ciperoensis S. distentus R. umbilicus E. formosa D. barbadiensis D. saipanensis ? ? I >23.9 NP25 24.5 >27.5 Preliminary interpretation of the magnetic inclination record identi- NP24 29.9 100 31.5 fied 64 reversals of the geomagnetic timescale in the sediment section. NP23

200

Although the Pliocene–Pleistocene section (0–5 m.y.) is apparently Oligocene 32.3 II Depth (mbsf) 300 missing, the barren pelagic sediments in the top 29 mbsf provided an NP22

32.8 excellent record from the Thvera Subchron (C3n.4n) through the late 400 NP21

34.3 NP19/

and middle Miocene polarity intervals to Subchron C5Bn.1n or close to Eocene 500 NP20 the base of the middle Miocene (Fig. F25). Major unconformities are Basement present between 14.8 and 24.1 Ma and in the top section of Biozone NP24 at ~25–30 Ma. Surprisingly, the magnetic inclination record in F25. Magnetic inclination and the turbidites between 100 and 500 mbsf defines several long normal declination record in pelagic sedi- and reversed polarity chrons (C12n–C16n.2n) that are well constrained ments, p. 57.

Biostrat. by biostratigraphic ages. The combined biostratigraphic and paleomag- Hole 1201B datum Depth Age Age (Ma) (mbsf) Polarity (Ma) Subchron Chron Epoch (Ma) 0 5 0.98 5.894 C3An.1n C3An netic results show that the sedimentation rates were moderate (35 m/ 6.567 C3An.2n 3.78 7.432 C4n.1n Pliocene C4n.2n C4n 5.78 8.072 C4r.1n C4r C4An m.y.) in the late Eocene, then very high (109 m/m.y.) in late Eocene– late C4Ar.1n C4Ar 10 9.63 9.740 C5n.1n C5n.2n C5n early Oligocene time, when the turbidites were being deposited, and 12.27 10.27 10 C5An C5An Miocene 14.63 12.401 C5Ar then decreased to very low values (3 m/m.y.) during the Miocene, when 17.63 12.991 C5AAn 13 C5AAn 20 19.83 13.703 C5ACn C5ACn

21.73 14.178 middle 14 the pelagic sediments at the top of the section were being deposited C5ADn C5ADn 24.12 14.800 C5Bn.1n

C6Cn.3n 24 (Fig. F26). Depth (mbsf) C6Cr 30.00 30 24.730 C7n.1n

(24.5) C7n Although the age of the basement could not be determined aboard (>23.9) C7n.2n

35.10 25.183 late 25

D. bisectus D. ship, its composition and provenance are clear. The 90 m of basement ciperoensis S. 40 drilled at Site 1201 consists of altered pillow basalts having a composi- Oligocene tion that is transitional between that of arc tholeiites and MORB and 50 -60 0 60 0 120 240 360 backarc basin basalts (Fig. F27). Geochemical and thin section analysis Inclination (°) Declination (°) SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 22 shows that the basalts have been strongly weathered, especially at the F26. Sedimentation rates at Site contact with the overlying sediments, where they show significant Na 1201, p. 58.

Pleist. Pliocene Miocene Oligocene Eocene uptake and depletion in Ca. Hyaloclastites in the section have been ccss s s gg lateearly late middle early late early late middle 0

LO S. ciperoensis 10-m.y. Miocene/Oligocene unconformity palagonitized and altered to smectite, and interpillow sediments recov- Sedimentation rate (14.8-24.1 Ma) late Oligocene unconformity? = 3 m/m.y. LO S. distentus ered from within the upper 10 m of basement contain marine microfos- 100 FO S. distentus sils, indicating eruption in a marine environment. Magnetic inclina- 200

Sedimentation rate tions in the basaltic basement are shallow and indicate a position of the = 109 m/m.y. LO R. umbilicus 300 Depth (mbsf)

Philippine plate near the equator, at ~7° paleolatitude, during the sand and siltstones Turbiditic

LO E. formosa Eocene. 400

Biostratigraphic datum (FO and LO) Sedimentation rate From the data provided above, it is evident that the basement at Site = 35 m/m.y. LO D. barbadiensis 500 Age-depth curve constrained by magnetostratigraphy + +

+ Altered pillow basalt

+ + 1201 formed near the equator by submarine eruption during the 0 5 10 15 20 25 30 35 40 Age (Ma) Eocene before 34.3 Ma. The composition of the basalts, which are transitional between island arc tholeiites and MORB or backarc basin basalts, suggests they erupted in an arc or backarc setting. The absence of F27. V vs. Ti tectonic discrimina- calcareous nannofossils and the presence of siliceous microfossils in the tion diagram, p. 59. interpillow sediments and pelagic sediments immediately overlying the 600 Ti/V = 10 Ti/V = 20 Hole 1201D basement suggests that the basement formed in a deep water environ- Basalt 500 Hyaloclastite Arc ment below the carbonate compensation depth (CCD) (Fig. F28). tholeiite 400 Ti/V = 50 MORB Beginning in the late Eocene and continuing into the early Oli- and BABB 300

gocene (from ~35 to 30 Ma), pelagic sedimentation at the site became V (ppm) OIB Ti/V = 100 mixed with, and was finally overwhelmed by, increasingly thick, coarse, 200 and energetic turbidites composed of arc-derived volcaniclastics and 100 reef detritus. The composition and timing of the turbidites is consistent 0 0 5 10 15 20 25 with a source to the east in the Kyushu-Palau Ridge, which was an ac- Ti (ppm)/1000 tive arc from ~48 to 35 Ma (Arculus et al., 1995) and only began to sub- side at ~28 Ma (Klein and Kobayashi, 1980). The presence of scoria and F28. Geological interpretation of rounded lithic clasts in the volcaniclastic breccia at Site 1201 is consis- the sediment and basement sec- tent with subaerial erosion, but the absence of plutonic fragments indi- tion, p. 60. cates that the ridge remained undissected (Dickinson, 1985; Valloni, SITE 1201 4. Pelagic sedimentation late Oligocene to early Pliocene 1985). The upward coarsening of the turbidites can be attributed to eolian many possible causes, including changes in arc elevation and erosion, W Palau-Kyushu E Ridge area of active sediment supply, proximity to source, tectonics, sea level, and slope gra- magmatism 3. High-energy turbidites dient. Alteration of the volcaniclastics would have commenced imme- late Eocene to early Oligocene increased subaerial (subaqueous?) diately after deposition and is continuing to the present in the upper volcanic relative progradation? activity? sea level fall? possible change in volcaniclastic source material part of the section, but diagenesis would only have begun when the tur- W (e.g., tuff to lapilli [more effusive rocks] E or increase in erosion of source volcano) burial diagenesis bidite section became sufficiently thick for the temperature in the lower 2. Low-energy turbidites late Eocene part of the section to reach 85° to 125°C (Fisher and Schminke, 1984). subaerial relative and sea level rise? subaqueous volcanic Between the late Oligocene and early Pliocene, the Kyushu-Palau fringing reef activity backarc (carbonate source) rifting? dominated by explosive W production of vitric ash E ? subsidence associated Ridge subsided, the deposition of turbidites came to an end, and pelagic with rifting? 1. Quiescent marine late Eocene eolian? sedimentation resumed at Site 1201 as the Parece Vela Basin opened terrestrial weathering? and arc volcanism moved eastward relative to the Kyushu-Palau Ridge W E

+ weathering in response to plate reorganization. Finally, even pelagic sedimentation + of basalt? + ceased at ~5 Ma, presumably in response to bottom currents caused by a change in bottom-water circulation.

SITE 1202: KUROSHIO CURRENT

The Kuroshio (Black) Current is the biggest western boundary surface current in the western Pacific. Because of its high speed (2.7–3.6 km/ hr), great thickness (1.0 km) and width (150–200 km), and high temperature (28°–29°C in summer and 22°–25°C in winter), it plays an important role in the meridional transport of heat, mass, momentum, and moisture from the western Pacific warm pool to high latitudes in the north Pacific. Although its role in the Pacific is as important as that of the Gulf Stream in the North Atlantic, almost nothing has been learned SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 23 about its evolution during the past 32 yr of drilling by DSDP and ODP because there are almost no locations beneath the Kuroshio Current where a deep-sea sedimentary section with high sedimentation rates can contain well-preserved calcareous microfossils. Because the CCD is shallow in the western Pacific (<3500 m) and the water depth is great (generally >4000 m), foraminifers and calcareous nannofossils are rarely preserved. Conditions appear to be ideal for obtaining a such a section, however, in the southern Okinawa Trough. As the Kuroshio Current passes between the eastern side of the island of Taiwan and the southernmost part of the Ryukyu Island arc, it is deflected upward when it approaches the Ilan Ridge and then flows northeastward in the Oki- nawa Trough (Ono et al., 1987; Chen et al., 1992) (Fig. F29). The seaf- F29. Location of Site 1202 in the loor in the Okinawa Trough lies above the CCD, and sedimentation Okinawa Trough, p. 61. rates are high because of terrigenous input from the East China Sea km shelf and the island of Taiwan (Boggs et al., 1979; Lin and Chen, 1983). 0 50 100 26° Upwelling Site 1202 was accordingly proposed on the southern slope of the Oki- N nawa Trough to obtain a high-resolution record of the history of the t ren 600 ur C 0 0 Kuroshio Current during the Quaternary. Keelung 0 1 o 25° Taipei i Okinawa Trough h s 1800 o r KS-1Site u 1202 1400 K 00 Taiwan 10

600

Geologic Setting 6 0 0 200 10 2800 00 24° The Okinawa Trough, which extends from southwestern Kyushu, 121°E 122° 123° 124° Japan, to the northeastern side of the island of Taiwan, is an active, incipient, intracontinental backarc basin formed behind the Ryukyu arc- trench system in the western Pacific (Lee et al., 1980; Letouzey and Kimura, 1985; Sibuet et al., 1987). The trough was formed by extension within continental lithosphere already intruded by arc volcanism (Uyeda, 1977; Sibuet and Hsu, 1997). Although there is considerable controversy about the age of early rifting, most researchers agree that the most recent phases of extension have taken place since 2 Ma (Sibuet et al., 1998). The southernmost part of the Okinawa Trough is characterized as a rifting basin with incipient arc volcanism opening in the middle of a foundered orogen caused by previous arc-continent collision (Teng, 1996). The recent phase of extension of the Okinawa Trough occurred in the late Pleistocene (~0.1 Ma) (Furukawa et al., 1991), based on seismic correlation with drilling stratigraphy (Tsuburaya and Sata, 1985), but the exact timing of this recent phase of extension in the area of the site is unknown. The extension is characterized by normal faulting on both sides of the trough. The amount of extension during this recent phase has been estimated to be 5 km, both in the middle and the southwest end of the Okinawa Trough (Sibuet et al., 1995, 1998). Based on the co- incidence in timing between the development of the sedimentary basins in the Okinawa Trough (Kimura, 1985) and the uplift of the Ryukyu arc at the Pliocene/Pleistocene boundary (Ujiie, 1980), Sibuet et al. (1998) concluded that the penultimate phase of rifting, including subsidence and block faulting along the central axis of the trough, started at ~2 Ma. The total amount of extension in the area is ~30 km. It has been suggested that the Okinawa Trough changed from an open-sea environment to a semienclosed marginal basin because of a 120-m drop in sea level (Fairbanks, 1989) during the last glacial maximum (Ujiie et al., 1991). Consequently, the Kuroshio Current may have been located on the trench side of the Ryukyu arc until ~7.5 ka during the Holocene (Ujiie et al., 1991; Ahagon et al., 1993; Shieh and Chen, 1995). Glacial–interglacial sea level fluctuations are likely to have caused significant changes in the configuration and distribution of continental shelves in the region, particularly in the South China Sea, and SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 24 these changes must have caused dramatic hydrographic changes and sediment redistribution in the Okinawa Trough. The southern Okinawa Trough is currently an area of high sedimentation because of the enormous terrigenous sediment supply from the East China shelf and the island of Taiwan. Modern sediments in this area consist mainly of clay- to silt-sized terrigenous sediments with a moderate (~20%) biogenic carbonate content (Chen et al., 1992; Lou and Chen, 1996). Sediment trap studies in the southern Okinawa Trough (Hung et al., 1999) indicate that the abundance of suspended particulate material decreases with increasing distance from the East Asian continent but increases with depth, implying effective resuspen- sion and lateral transport across the area. Studies of short piston cores (Lou and Chen, 1996; Shieh et al., 1997; Ujiie and Ujiie, 1999) taken from the area suggest that sedimentation rates during the Holocene were ~20 cm/ky. Extensive geophysical surveys conducted in the area (Sibuet et al., 1998; Liu et al., 1998) show that the trough is marked by a series of normal faults dipping toward the center and a series of volcanic edifices and hydrothermal vents piercing through the sedimentary layer. Based on low interval velocities (<2.0 km/s) determined from the analysis of seismic data, a prominent series of reflectors is observed from 250 to 350 mbsf (Fig. F30). This prominent reflection has been suggested to be F30. North-south seismic profile the unconformity marking the onset of the most recent phase of exten- EW95091 at Site 1202, p. 62.

Shotpoint sion of the Southern Okinawa Trough (Hsu, 1999). Site 1202 was pro- 1829 1816 1800 1786 1773 1760 1746 1734 1721 1709 1697 1685 1673 1662 1650 1639 1627 1616 1605 1593 1582

1.5 S N posed to penetrate this sequence to a depth of ~410 mbsf, not only to 1 km Site 1202 study the paleoceanography of the Kuroshio Current but to provide constraints on the timing of the most recent phase of extension in the 2.0 Okinawa Trough. 2.5 Two-way traveltime (s) traveltime Two-way Scientific Objectives 3.0

3.5 The primary objective of drilling at Site 1202 was to obtain a high- Line EW9509-1 resolution record of the paleoceanographic history of the Kuroshio Cur- rent. Such a record might make it possible to identify long-term patterns of climate change associated with the western Pacific boundary current during the past 1.5 m.y. For example, the Kuroshio Current passes over the Ryukyu arc and into the Okinawa Trough before turning northeast and continuing toward Japan, but changes in sea level associated with glacial–interglacial cycles could well redirect the Kuroshio Current outside the arc and isolate the Okinawa Trough on a cyclic basis. Changes in sedimentation caused by such deflections, coupled with periodic exposure of the continental shelf to the northwest during low sea level stands, should be easily detectable by drilling at Site 1202. We also hoped that drilling at Site 1202 would enable us to detect the effects of orbital forcing in the Pacific during the mid-Pleistocene (~0.7 Ma), when the Earth’s climate system switched from a regime of dominant 41-k.y. cycles to 100-k.y. cycles. Oxygen isotope measurements on foraminifers from Site 1202, for example, should reflect surface temperature cycles over a large area of the western equatorial Pacific because the Kuroshio Current is a composite current assembled from numerous smaller currents before it reaches the site. We also hoped to document the temporal and spatial variability of millenial climate changes in the Kuroshio Current and the catchment basins that deliver sediments to the Okinawa Trough. These changes should be reflected not only in the oxygen isotopic composition of microfossils but in the grain size and composition of sediments from some SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 25 of the largest river systems in east Asia, including the Yangtze, which rises in Tibet and samples much of southern China. Finally, we hoped to examine long-term changes in El Niño/La Niña– style climate oscillations in the low-latitude Pacific by comparing the Kuroshio Current record to other Pacific ODP records (Andreasen and Ravelo, 1997; Clement et al., 1999).

Drilling Strategy and Operations

After arriving on station and lowering the pipe, we planned to triple– APC core the sediment section to refusal, which was estimated to be at ~250 mbsf, to obtain overlapping, and thus complete, coverage for high-resolution paleoenvironmental studies. If time allowed, we planned to deepen the third hole to 410 mbsf using the XCB. We then hoped to log the open hole using the triple combo and the FMS-sonic tools to provide a quantitative basis for comparison with the multisensor track (MST) data, which could be used to reconstruct a continuous sediment section for the site. The transit to Site 1202 (proposed Site KS-1) was made in good time with fair seas and favorable currents. The 784-nmi distance was covered in 64.9 hr at an average speed of 12.1 kt. At 0254 hr on the morning of 28 April, the vessel arrived at 24°48.24′N, 122°30.00′E, the coordinates for the drilling location. The crew began lowering thrusters and hydro- phones, and at 0515 hr on 28 April the positioning beacon was deployed. A standard APC/XCB bottom-hole assembly (BHA), including a lock- able float valve (LFV) to allow wireline logging of the deepest hole of the site, was made up. The drill string was tripped to the bottom, and Hole 1202A was spudded at 0810 hr. APC coring continued through Core 195-1202A-9H to a depth of 83.1 mbsf (Table T1) when the APC failed to stroke out. Core 195-1202A-10H fully stroked; however, Cores 11H and 12H did not fully advance. Advance by recovery was used for the two incomplete cores in the hope that the hard layer would be limited in thickness and piston coring would once again become viable. APC refusal was finally accepted when Core 195-1202A-13H at 119.5 mbsf had not only failed to scope, but the core liner failed at the mid- point of the barrel. Core orientation using the Tensor tool was initiated with Core 195-1202A-4H and continued through Core 13H. Tempera- ture measurements were taken on Cores 195-1202A-4H, 7H, 10H, and 13H using the Adara temperature tool. Two of the four temperature measurements were good (see “Physical Properties,” p. 11, in the “Site 1202” chapter). The developmental APC-methane tool was deployed on Core 195-1202A-4H and then on Cores 7H through 13H. All runs were successful in acquiring data. Hole 1202A officially ended with the clear- ing of the seafloor at 1900 hr on 28 April. The vessel was offset 15 m to the east, and Hole 1202B was spudded at 1935 hr on 28 April. APC coring continued through Core 195-1202B- 13H to a depth of 111.6 mbsf (Table T1) before APC refusal was defined by two successive incomplete strokes on Cores 195-1202B-12H and 13H. Because the ultimate depth objective at this site was 410 mbsf, we decided to cut three XCB cores before terminating the hole to obtain an idea about penetration rates, core recovery, and quality. Coring continued with the XCB through Core 195-1202B-16X to a depth of 140.5 mbsf. The drill string was pulled clear of the seafloor, officially ending Hole 1202B at 0445 hr on 29 April. SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 26

The ship was offset 15 m to the east, and Hole 1202C was spudded at 0540 hr on 29 April. APC coring continued through Core 195-1202C- 11H to a depth of 97.5 mbsf (Table T1), where APC refusal was encountered as defined by three consecutive incomplete strokes. Core orientation using the Tensor tool was initiated with Core 195-1202C-4H and continued through Core 11H. The drill string was pulled clear of the seafloor, officially ending Hole 1202C at 1215 hr on 29 April. For the third time, the ship was offset 15 m to the east, and Hole 1202D was spudded with the APC at 1245 hr on 29 April. Recovery of the first core was only 15 cm. APC coring continued in this hole through Core 195-1202D-9H to a depth of 76.2 mbsf (Table T1), when the first core did not achieve full stroke. Coring with the XCB proceeded through Core 195-1202D-32X to a depth of 297.4 mbsf, where a short wiper trip was made to 221.3 mbsf, above an area of poor recovery. The wiper trip was uneventful, and coring continued through Core 195-1202-44X to a depth of 410.0 mbsf, the approved target depth for Site 1202. In preparation for logging, a wiper trip was initiated at 1930 hr on 30 April and reached the logging depth of 80.0 mbsf without incident. The hole was displaced with 150 bbl of sepiolite logging mud, and the bit was pulled back to a logging depth of 80.0 mbsf. The triple combo tool string was made up with the Lamont Doherty Earth Observatory (LDEO) temperature/acceleration/pressure (TAP) tool. A nuclear source was not incorporated because the loss of density data did not outweigh the risk of losing the source in disputed waters under hostile current conditions. Throughout operations at the site, the Kuroshio Current was strong. Heavy pipe vibration was experienced continually, while the currents varied cyclically between 2.6 and nearly 4.0 kt. The first tool string was deployed to a depth of ~215 meters below rig floor. At that point, the logging engineer reported losing all power to the logging tools. After bringing the tool string to the surface, the tools showed several loose connections caused by the current- induced drill sting vibrations. All joints were retightened and taped with duct tape. The tool string was once again deployed inside the drill pipe; however, the winch operator only reached 72 mbsf before losing weight with the logging line, as if setting down on an obstruction. Upon recovery, the connections were once again found to be loose and the lower portion of the TAP tool was missing. At 0430 hr, the circulating head was rigged up and the coring line was run in the hole to determine if the TAP tool was lodged in the drill string. Results were inconclusive. We decided to abandon further wireline logging efforts because of the intensity of the current-induced drill string vibration. The drill string was pulled clear of the seafloor by 0730 hr. By 1100 hr, preparations were under way to secure and clean the ship for transit into port. The ~55-nmi transit to Keelung, Taiwan, was made at reduced speed for an 0815-hr arrival at the pilot station on 2 May 2001. The ship was dockside at 0904 hr, ending Leg 195.

Principal Results

The principal objective at Site 1202 was to obtain a continuous sediment section deposited beneath the Kuroshio Current that would allow high-resolution studies of climate change in East Asia associated with late Quaternary glaciation and deglaciation cycles. The strategy adopted was to drill at an extremely high sedimentation rate site in relatively SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 27 shallow water above the CCD in the Okinawa Trough where calcareous microfossils would be preserved in an expanded section. The objective was met with the recovery of a 410-m section of dark grayish green, bioturbated clayey silt with abundant sandy turbidites between 220 and 280 mbsf and occasional thin (<1 cm) turbidites scat- tered throughout the rest of the section. The sediments were rich in organic carbon and charged with H2S. Smear slide analysis shows that the nonbiogenic component of the sediments is composed predominantly of quartz, feldspar, and detrital carbonate, whereas the turbidites also contain micas, heavy minerals (green hornblende, tourmaline, epidote, and zircon), and opaques. Surprisingly, no tephra layers were observed and glass shards are rare. Although the site is located in the Okinawa Trough, heat flow values (0.040 W/m2) were slightly lower than the global average and no evidence of diagenesis was observed. As anticipated, the preservation of calcareous microfossils was excellent, with planktonic and benthic foraminifers and calcareous nannofossils present in small amounts (<1% by volume) throughout the section, except in the turbidites, where they are abundant. Also present, especially in the turbidites, are diatoms, ostracodes, radiolarians, sponge spicules, the plates and spines of echinoderms, fragments of molluscs and pteropods, copepod remains, and fragments of bark, roots, and leaves, the latter indicating rapid burial and high sedimentation rates. Despite the excellent preservation of microfossils, shipboard determination of the age of the section proved difficult. The presence of Emil- iania huxleyi throughout the section suggests that the section is very young (<0.26 Ma, or latest Quaternary) and the absence of pink G. ruber indicates that the entire section is younger than 127 ka. This is consistent with shipboard paleomagnetic inclination data, which shows that the entire 410-m section lies within the Brunhes C1n normal polarity chron and is thus <0.78 Ma in age. Several excursions are seen in the data, including one at 110 m, which may correspond to the Laschamps event (40–45 ka), but given the absence of biostratigraphic markers and reversals, an accurate age determination for the section will have to be based on paleointensities. If the age of the section is <127 ka, as suggested by the absence of pink G. ruber, then the sedimentation rate at the site was at least 3 m/ k.y., one of the highest rates ever observed in the ocean basins for fine- grained, fossiliferous sediments. Given the relatively low biogenic content of the sediments, this requires a large terrigenous source. We infer that the section is composed of reworked sediments from the Chinese mainland that were delivered to the East China shelf by the Yangtze River. The presence of mica and other metamorphic minerals in the coarse fraction of the turbidites suggests that an additional component is derived from nearby metamorphic terrains on the island of Taiwan. If this initial interpretation is borne out, then the section recovered at Site 1202 is almost ideal for studying climate change associated with glaciation and deglaciation in East Asia during the Holocene and latest Pleistocene. The section is relatively homogeneous; it is continuous, at least in the top 130 m where it was APC cored; it contains excellent paleomagnetic, lithologic, and biogenic proxies for climate; and it displays extraordinarily high resolution (<100 yr, assuming bioturbation to 20 cm). In principle, this resolution should be sufficient to study the influence of climate on the rise of Chinese civilization. SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 28 REFERENCES

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Tsuburaya, H., and Sata, T., 1985. Petroleum exploration well Miyakojima-Oki. J. Jap- anese Assoc. Petrol. Technol., 50:25–53. Ujiié, H., 1980. Significance of “500 m deep island shelf” surrounding the southern Ryukyu Island arc for its Quaternary history. Quat. Res., 18:209–219. Ujiié, H., Tanaka, Y., and Ono, T., 1991. Late Quaternary paleoceanographic record from the middle Ryukyu Trench slope, northwest Pacific. Mar. Micropaleontol., 18:115–128. Ujiié, H., and Ujiié, Y., 1999. Late Quaternary course changes of the Kuroshio Current in the Ryukyu arc region, northwestern Pacific Ocean. Mar. Micropaleontol., 37:23– 40. Uyeda, S., 1977. Some basic problems in trench-arc-back-arc systems. In Talwani, M., and Pitman, W.C., II (Eds.), Island Arcs, Deep Sea Trenches, and Back-arc Basins. Geo- phys. Monogr., Maurice Ewing Ser., Am. Geophys. Union, 1:1–14. Valloni, R., 1985. Reading provenance from modern marine sands. In Zuffa, G.G. (Ed.), Provenance of Arenites. NATO ASI Ser. C, 148:309–332. van der Hilst, H., Engdahl, R., Spakman, W., and Nolet, G., 1991. Tomographic imaging of subducted lithosphere below northwest Pacific island arcs. Nature, 353:37– 43. van der Hilst, R.D., and Seno, T., 1993. Effects of relative plate motion on the deep structure and penetration depth of slabs below the Izu-Bonin and Mariana Island arcs. Earth Planet. Sci. Lett., 120:395–407. White, A.F., and Hochella, M.F., 1992. Surface chemistry associated with the cooling and subaerial weathering of Recent basalt flows. Geochim. Cosmochim. Acta, 56:3711–3721. Zhang, Y.S., and Tanimoto, T., 1992. Ridges, hotspots and their interaction as observed in seismic velocity maps. Nature, 355:45–49. SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 33

Figure F1. Location map showing sites drilled during Leg 195. The geochemical observatory was installed at Site 1200, and the International Ocean Network (ION) seismic observatory was installed at Site 1201. Site 1202 was drilled to study the history of the Kuroshio Current.

30° N

Keelung 1202 25°

Altitude/ Depth (m) 4000 20° 2000 1201 0

2000 ° 15 1200 4000 km Guam 6000 0 200 400 8000 10° 110°E 115° 120° 125° 130° 135° 140° 145° 150° SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 34

Figure F2. Bathymetric map of the southern Mariana forearc (250-m contour intervals) showing locations of all forearc seamounts sampled to date. Site 1200 was drilled on South Chamorro Seamount during Leg 195. 144°E 146° 148° ° 20 Conical Seamount N

4000 2000 Pacman Seamount

4000 4000 2000

Pagan Big Blue Seamount 18°

8000

4000 4000 2000

8000 Turquoise Seamount

4000 Celestial Seamount

2000 2000 16° Peacock Seamount 6000 Blue Moon Seamount

4000 Saipan

2000

4000

° 14 North Chamorro Seamount Guam 8000

6000

2000 6000

4000 8000 South Chamorro Seamount

6000 12°

100 km SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 35

lting Depth (km) Depth 0 10 20 of ~15 and 20 and ~15 of bduction both play a both bduction both the décollement both

Legend Conduit of mud volcano Conduit of mud Dip-slip motion Horizontal motion away Horizontal motion toward Pods of blueschist Pods Serpentine volcano mud 0

Pacific plate Seamount Pacific

dessication,

compaction, compaction,

diagenetic reactions diagenetic

Low- to intermediate-grade metamorphism, metamorphism, intermediate-grade to Low-

Direction of subduction of Direction

Horst block u

u S

Distance from trench axis (km)

reactions dehydration Graben

Forearc sediment Forearc

decarbonation,

Blueschist metamorphism, Blueschist

collement

é Schematic cross section through the Mariana system showing various types of associations of serpentine mud volcanoes, with fau with mud volcanoes, serpentine of associations types of various showing system Mariana the through section cross Schematic D 100 50 Horst block Figure F3. Figure seamount su to related tectonics and vertical extension along-strike with associated faulting the forearc Strike-slip wedge. in and from gouge of fault of forearc slab-derived fluids provide the ascent avenues for the and the tectonic deformation part in and the lithosphereoverriding of the plate. Decarbonationreactions the in downgoing plateprobablytakeplace between depths km. SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 36

Figure F4. HMR-1 side-scan imagery of South Chamorro Seamount showing the locations of six-channel seismic reflection profiles shown in Figure F5, p. 37. Contour intervals are given in meters. 145°45´E 146°00´ 146°15´ 146°30´ 14°50´ N

Fault block North Chamorro Seamount

14°00´

4000 4000

South Chamorro Summit knoll Seamount A 4000 B'

5000 6000

13°45´ 4000 B Site A' 1200 Debris flows 7000

8000

13°30´

8000 7000

5000 7000

8000 8000 9000

° 13 15´ 6000 7000 Fault scarps

9000

Fault block 13°00´ 0 50

km SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 37 SE p. 36). F4, km B' NE Site 1200 (location is 2 km SW of this point) 010 Site 1200 NW (location is 3.5 km SE of this point)

4 5 6 7 8 9 AA' Two-way traveltime (s) traveltime Two-way Multichannel seismic reflection profiles over South Chamorro Seamount (locations are shown Fig. in SW

4 5 6 7 8 B Two-way traveltime (s) traveltime Two-way Figure F5. Figure SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 38

Figure F6. Locations of Holes 1200A–1200F drilled on the summit knoll of South Chamorro Seamount. Also shown is the location of the seafloor television survey conducted before drilling. Contours are given in meters. 13°47.2´ N

2980

2970

5 4 C D

° F 6 13 47.0´ A 2 EB1,3

2960

2970

2990 3000 2980

2990 3000 13°46.8´ 146°0.0´E 146°0.2´ 146°0.4´ 0 0.2

km SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 39

Figure F7. Casing configuration for the geochemical observatory installed in Hole 1200C on South Chamorro Seamount. Top of reentry cone 2940.6 m

Seafloor depth 2943.0 mbrf

20-in casing shoe 23.7 mbsf 16-in casing shoe 107.4 mbsf

Top of 10.75-in Perforated and screened casing screened casing 148.8 mbsf 53.5 m Bottom of 10.75-in 10.75-in casing shoe screened casing (flapper sealed with Baker-loc) 202.3 mbsf 202.8 mbsf Open hole

9 m of fill in bottom of hole Total depth of hole 266.0 mbsf SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 40

Figure F8. Geochemical observatory (CORK) configuration in Hole 1200C, South Chamorro Seamount.

Data logger Reentry cone Depth (mbsf) 0.0 Seafloor 0.3 Stinger 23.7 6 joints 20-in casing 5.5 in K-55, buttress 94 lb/ft 29.0 Stinger T10 58.0 reentry Cement 64.0 sub T9 Thermistor cable 15.8 lb/gal 87.0 T8 107.4 16-in casing 110.0 Spectra line T7 K-55, buttress 115.0 T6 75 lb/ft 120.0 T5 125.0 T4 130.0 T3 132.0 T2

Extension cable

137.0 Osmotic sampler 2 142.0 142.5 10.75-in casing Osmotic K-55, buttress 147.5 sampler 1 40.5 lb/ft 149.0 Weak point

Osmotic Spectra line sampler 1 171.0 intake 174.0 Sinker bar 176.0

202.3 10.75-in screen, K-55, buttress, 40.5 lb/ft 312.5-in holes/ft wrapped with 0.090-in diameter wire with 0.008-in gap over 266.0 0.125-in standoff rods SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 41

Figure F9. Close-up photograph of serpentine mud breccia from South Chamorro Seamount (interval 195- 1200E-10H-2, 83–113 cm). cm

100

105

110 SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 42

Figure F10. Photomicrograph of glaucophane (Gl) schist in serpentine mud (Sample 195-1200F-1H-4, 34– 36 cm).

0.25 mm SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 43

Figure F11. Photomicrograph of tremolite (Tr)-rich chlorite (Chl) schist in serpentine mud (Sample 195- 1200F-1H-4, 34–36 cm).

Chl

0.5 mm SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 44

2+ 2+ 2+ Figure F12. (A) Al2O3 and (B) Mg /(Mg +Fe ) diagrams for Mariana forearc peridotites, showing degrees of partial melting. Conical and Torishima Forearc Seamount data are from Ishii et al. (1992) and Parkinson and Pearce (1998). A 1 30% melting

0.8 Conical Seamount peridotites

0.6 (wt% rock) 3 0.4 O 2

Al Torishima Seamount peridotites

0.2 South Chamorro Seamount peridotites

15% melting 0 0 0.5 1 1.5 2 2.5 CaO (wt% rock) B 90

30% melting Conical Seamount peridotites 91 ) rock 2+

92 + Fe

/(Mg 93 2+ Torishima Seamount peridotites Mg × South Chamorro 94 100 Seamount peridotites

15% melting 95 0 0.5 1 1.5 2 2.5 CaO (wt% rock) SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 45 Boron. Arrow = D. Sulfate (mmol/kg) Sulfate E Sodium/chloride. Sodium/chloride. C. mol/kg) Alkalinity. Alkalinity. µ B. pH. pH. Boron ( A. D Na/Cl (mol/mol) Alkalinity (mmol/kg) BC pH Hole 1200D Hole 1200E Hole 1200F Hole 1200A Pore water composition vs. depth curves for Holes 1200D, 1200E, and 1200F. 1200F. and 1200E, 1200D, Holes for curves depth vs. composition water Pore 8 9 10 11 12 13 0 40 80 120 0.8 0.9 1 1.1 1.2 1.3 0 2000 4000 0 10 20 30 0

10 20 30 40 50 60 70 80 Sulfate. Hole 1200E is closest to the vent community on the summit of South Chamorro Seamount; Hole 1200D is the most distant. most is the 1200D Hole Seamount; Sulfate.Chamorro of South summit the on community vent the Holeto is closest 1200E (mbsf) Depth A E. seawater value. Figure F13. Figure SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 46

Figure F14. Location of seismic station coverage in the northwest Pacific region. At least five major plates with consuming boundaries interact in the northwest Pacific, causing subduction, backarc spreading, slab collisions, terrane accretion, and island arc development. Blue and yellow circles = land seismic stations. Orange circles = International Ocean Network (ION) seafloor observatories JT-1 and JT-2 (Japan Trench), WP-2 (northwest Pacific), and Site 1201 (this site). OHP = Ocean Hemisphere Network Project, IRIS = Incor- porated Research Institutions for Seismology. TJN = Taejon, South Korea; INU = Inuyama, Japan; ISG = Ish- igakijima, Japan; OGS = Chichijima, Japan; MCSJ = Minami Torishima, Japan; BAG = Baguio, Philippines; PATS = Pohnpei, Micronesia; JAY = Jayapura, Indonesia; PMG = Port Moresby, Papua New Guinea.

40° WP-2 N JT-1 INU TJN JT-2

ISG OGS MCSJ 20° BAG 1201

PATS

0° JAY

km PMG 0 500 1000

100°E 120° 140° 160° 180°

ION seafloor borehole station Current OHP land station Past OHP land station IRIS land station SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 47

Figure F15. Location map showing DSDP Sites 290, 294, 295, and 447 and ODP Site 1201 in the Philippine Sea. Also shown are magnetic lineations from Hilde and Lee (1984). Basement ages in parentheses. The Central Basin Fault (the former spreading center) is shown as a series of heavy solid lines with offsets along transform faults. 25° (57±1) N 22 24 21 Taiwan16 17 23 294 20 17 18 295 18 22 (49±2) 24 19 19 19 21 23 18 16 19 20 21 14 22 20 18 20° 14 16 17 19 20 1201 13 16 21 17 14 18 21 22 17 19 447 14 16 16 18 19 18 (43) 290 16 14 17 18 19 17 16 16 19 14 17 19 18 17 16 18 20 18 14 14 17 16 Kyushu-Palau Ridge 19 14 1416 ° 20 17 16 15 21 1413 18 17 16 20 18 17 19 18 21 20 19 19

anomaly 13 20 Altitude/ 35 14 21 West 15 Philippines Depth (m) 16 Philippine 40 17 21 Sea 4000 10° 18 45 19 22 2000 20 23 21 0 50 24 22 2000 23 25 55 24 26 4000 25 60 26 km 6000 Ma 8000 0 200 400 5° 120° E 125° 130° 135° 140° SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 48 NE km 012 800 900 1000 Site 1201 CDP number 700 Reflection line OT97 showing the location of Site 1201. Basement lies about 0.45 s (two-way traveltime) below seafloor and was and below seafloor 0.45 s traveltime) about lies (two-way 1201. Basement of Site location showing the line OT97 Reflection SW OT97 line 3 migrated OT97

600

7 8 9 Two-way traveltime (s) traveltime Two-way Figure F16. Figure reached at 510 mbsf. CDP = common depth point. depth = common CDP 510 mbsf. at reached SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 49

Figure F17. Borehole seismometer instrument package deployed in Hole 1201D. BIA = borehole instrument assembly, OBH = ocean borehole seismometer.

OBH (T1023[D003])

BIA

OBH (T1038[D417]) SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 50

Figure F18. Configuration of reentry cone, casing, and International Ocean Network seismic observatory components at Site 1201. MEG = multiple-access expandable gateway, ROV = remotely operated vehicle, PAT = power access terminal. Top of riser/hanger (8.1 m) J-tool to disconnect from drill string Casing hanger body Data control unit (MEG-195)

4.5-in through casing ROV platform (5.05 m)

Battery/recorder unit (PAT) Centralizing ring × 683-mm ID (top) 3200-mm diameter 2640-mm height (leg) 3658-mm diameter Centralizer

Top of reentry cone (2.41 m)

Reentry cone

Reentry cone base Seafloor (5721 mbsl)

Pelagic silty clay Landing point (0.3 mbsf)

16-in casing

Bottom of 16-in casing (39.0 mbsf)

54.0 mbsf Centralizer

Turbidites 10.75-in casing

Circulating sub cement level in 4.5-in casing (278.4 mbsf)

Cement level in 10.75-in casing (384.4 mbsf) Bottom of 10.75-in casing (527.0 mbsf) Bottom of 14.75-in rat hole (543.0 mbsf) 512.0 mbsf 9.875-in open hole Cement Basalt Bottom of 4.5-in casing (558.4 mbsf) Bottom of upper seismometer (561.2 mbsf) Bottom of lower seismometer (564.2 mbsf) Bottom of stinger (568.7 mbsf) Rat hole Bottom of 9.875-in hole (580.0 mbsf) SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 51

Figure F19. Remotely operated vehicle (ROV) landing platform installed in Hole 1201D. LBU = lithium battery unit, SAM = storage acquisition module, UMC = underwater mateable connector.

SAM frame

Top plate (ROV platform) 3.200 m

LBU 2

UMC cable LBU 1

3.658 m

2.640 m SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 52

Figure F20. Lithology, color, natural gamma count, and mineralogy vs. depth and age at Site 1201. Note the increase in zeolites with depth in the turbidites. In the graphic lithology log, c = clay, s = silt, s = sand, g = gravel. a* = color reflectance parameter.

Graphic lithology Lith. Color Natural log Age unit reflectance gamma radiation Mineralogy cssg 0 IA e. Plio. e.

50 Oligo. to l. IB IC

100 IIA

150

200

250 IIA

300 Depth (mbsf) 350 late Oligocene to Eocene

400 IIA 450

500 IIB + +

+ +

+ Illite 550 + + + Quartz Erionite + + Gypsum Pyroxene Phillipsite + Basaltic Chabazite basement + + Plagioclase + 600 -10 0 1020 0 10 20 30 Analcime/Wairakite green red a* (cps) Heulandite/Clinoptilolite ExpandableWell-crystallized clay minerals smectite SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 53

Figure F21. Laboratory multisensor track measurements of (A) magnetic susceptibility, (B) density, and (C) natural gamma ray emission vs. depth at Site 1201. In the graphic lithology log, c = clay, s = silt, s = sand, g = gravel. Graphic lithology Lith. log Age unit ABC cssg 0 IA

IB to l. Oligo. to l. l. Pliocene l. IC

100 IIA

200

IIA

300 late Oligocene to late Eocene Depth (mbsf)

400

IIA

500 IIB + +

+ +

+ + Basaltic

+ basement

+ + + 600 0 2000 1230102030 Magnetic susceptibility Density NGR (× 10-5 SI) (g/cm3) (cps) SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 54

Figure F22. Logging results from Hole 1201D. Logging Units 1a–1d correspond to coarse turbidite units. In the graphic lithology log, c = clay, s = silt, s = sand, g = gravel. * = spurious data. Density PorosityResistivity Velocity Hole diameter core core shallow core Graphic 020(in)(g/cm3) 0(%) 100 1(Ωm) 200 1500(m/s) 3500 lithology Gamma ray log log deep log log 3 Ω Core Recovery Depth (mbsf) Lith. unit Lith. 055(gAPI) 1(g/cm ) 3 0(%) 100 1( m) 200 1500(m/s) 3500 Logging unit cssg 0 IA

IB IC Pipe depth Pipe depth 1 1R 2R 100 3R a 4R IIA 5R 6R 7R 8R 9R 10R b 11R 12R 13R 200 14R 15R 16R 17R 18R c IIA 19R 20R 21R 22R 23R 300 * 24R 25R d 26R 27R 28R 29R 30R 31R * 32R Splice depth 33R 34R 400 35R * 36R IIA 37R 38R 39R * 40R 41R 42R 43R 44R 500 45R IIB 46R + + 47R + 2 + + 48R + 50R 49R + + 51R + 52R + +

Basaltic +

53R basement + + 54R + 55R 600 SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 55 Alkalinity (meq/kg) 0 0.5 1 1.5 2 2.5 Sodium (mmol/kg) Calcium (mmol/kg) ) alkalinity vs. depth in pore waters from Site 1201. In the graphic lithology log, c = clay, s = silt, s = silt, s s = = clay, c log, lithology graphic In the 1201. Site from waters in pore depth vs. alkalinity ) D 1201A 1201B 1201D (mmol/kg) Magnesium ) Na, and ( and ) Na, C 0 20 40 60 0 100 200 300 100 300 500 0 ABCD ) Ca, ( ) Ca,

100 200 300 400 500

B Lith. unit Lith.

IA IB

IIA IIA IIA

to l. Oligo. l. to IC

Age late Oligocene to late Eocene late to Oligocene late IIB l. Pliocene l. ) Mg, ( ) Mg, A ( log cssg Graphic lithology 0

100 150 200 250 300 350 400 450 500 Depth (mbsf) Depth Figure F23. Figure sand, g = gravel. Arrows = seawater values. g = sand, SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 56

Figure F24. Nannofossil ranges at Site 1201. The upper 25 m and the lower 45 m of the section are barren except for radiolarians and fish teeth. In the graphic lithology log, c = clay, s = silt, s = sand, g = gravel.

Graphic lithology log cssg Zone Age (Ma) Lith. unit Lith. 0 D. bisectus C. abisectus Z. bijugatus D. tanii ornatus B. serraculoides H. compacta S. pseudoradians S. predistentus S. ciperoensis S. distentus R. umbilicus E. formosa D. barbadiensis D. saipanensis ? ? I >23.9 NP25 24.5 >27.5 NP24 29.9

100 31.5

NP23

200 Oligocene 32.3 II Depth (mbsf) 300 NP22

32.8 400 NP21

34.3 NP19/

500 NP20 Eocene Basement SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 57

Figure F25. Continuous magnetic inclination and declination record in pelagic sediments at Site 1201 (large dots correspond to discrete samples). Also shown is the best fit to the late Oligocene through late Miocene geomagnetic polarity timescale based on paleontological markers from the site. In the polarity col- umn, black bands = normal and white bands = reversed polarity.

Biostrat. Hole 1201B datum Depth Age Age (Ma) (mbsf) Polarity (Ma) Subchron Chron Epoch (Ma) 0 5 0.98 5.894 C3An.1n C3An 6.567 C3An.2n 3.78 7.432 C4n.1n Pliocene C4n.2n C4n 5.78 8.072 C4r.1n C4r C4An C4Ar.1n late C4Ar 10 9.63 9.740 C5n.1n C5n.2n C5n 12.27 10.27 10 C5An C5An Miocene 14.63 12.401 C5Ar 17.63 12.991 C5AAn 13 C5AAn 20 19.83 13.703 C5ACn C5ACn

21.73 14.178 middle 14 C5ADn C5ADn 24.12 14.800 C5Bn.1n

C6Cn.3n 24 Depth (mbsf) C6Cr 30.00 30 24.730 C7n.1n

(24.5) C7n (>23.9) C7n.2n

35.10 25.183 late 25

D. bisectus D.

S. ciperoensis S. 40 Oligocene

50 -60 0 60 0 120 240 360 Inclination (°) Declination (°) SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 58

clay, s = s clay, Turbiditic sand and siltstones and sand Turbiditic Eocene late middle

R. umbilicus R.

S. distentus S. LO FO

D. barbadiensis D. late Oligocene unconformity? LO early

E. formosa E. LO

S. ciperoensis S. Oligocene Altered pillow basalt Altered pillow LO late Sedimentation rate = 109 m/m.y.

S. distentus S. Sedimentation rate = 35 m/m.y. LO Age (Ma) 10-m.y. Miocene/Oligocene unconformity 10-m.y. (14.8-24.1 Ma) Biostratigraphic datum (FO and LO) Biostratigraphic Sedimentation rate = 3 m/m.y. early Age-depth curve constrained by magnetostratigraphy by Age-depth curve constrained Pliocene Miocene late late middle early g Sedimentation rates at Site 1201 based on biostratigraphic and magnetostratigraphic results. In the graphic lithology log, c = c log, lithology graphic In the results. magnetostratigraphic and biostratigraphic on based 1201 Site at rates Sedimentation + + + css c s g + + Pleist. 0 5 10 15 20 25 30 35 40 0

100 200 300 400 500 Depth (mbsf) Depth Figure F26. Figure = gravel. sand, g s = silt, SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 59

Figure F27. V vs. Ti tectonic discrimination diagram for Site 1201 basalts. The basalts at Site 1201 are transitional between arc tholeiites and mid-ocean-ridge basalts (MORB) or backarc island basalts (BABB). OIB = ocean island basalt. 600 Ti/V = 10 Ti/V = 20 Hole 1201D Basalt 500 Hyaloclastite Arc tholeiite

400 Ti/V = 50 MORB and BABB 300 V (ppm) OIB Ti/V = 100 200

100

0 0 5 10 15 20 25 Ti (ppm)/1000 SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 60

Figure F28. Geological interpretation of the sediment and basement section at Site 1201. SITE 1201 4. Pelagic sedimentation late Oligocene to early Pliocene eolian

W Palau-Kyushu E Ridge area of active magmatism

3. High-energy turbidites late Eocene to early Oligocene

increased subaerial (subaqueous?) volcanic relative progradation? activity? sea level fall? possible change in volcaniclastic source material W (e.g., tuff to lapilli [more effusive rocks] E or increase in erosion of source volcano) burial diagenesis

2. Low-energy turbidites late Eocene

subaerial relative and sea level rise? subaqueous volcanic fringing reef activity backarc (carbonate source) rifting? dominated by explosive W production of vitric ash E ? subsidence associated with rifting?

1. Quiescent marine late Eocene eolian? terrestrial weathering?

W E

+ weathering + of basalt? + SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 61

Figure F29. Location of Site 1202 in the Okinawa Trough. The seafloor in the trough under the Kuroshio Current lies above the carbonate compensation depth. Diverging arrows indicate zones of upwelling. Con- tour interval = 200 m.

0 50 100

26° Upwelling N

t ren 600 ur C Keelung 1000 o 25° Taipei i Okinawa Trough h s 1800 o r KS-1Site u 1202 1400 K Taiwan 1000

600

600 200 2800 1000 24° 121°E 122° 123° 124° SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 62

Figure F30. North-south seismic profile EW95091 at Site 1202. Shotpoint 1829 1816 1800 1786 1773 1760 1746 1734 1721 1709 1697 1685 1673 1662 1650 1639 1627 1616 1605 1593 1582

1.5 S N 1 km Site 1202

2.0

2.5 Two-way traveltime (s) traveltime Two-way

3.0

3.5 Line EW9509-1 SHIPBOARD SCIENTIFIC PARTY CHAPTER 1, LEG 195 SUMMARY 63

Table T1. Coring summary, Leg 195.

Water Interval Core Core depth cored recovered recovery Hole Latitude Longitude Coring technique (mbsl) (m) (m) (%)

1200A 13°47.0053’N 146°0.1854’E RCB 2910 147.2 13.8 9.4 1200B 13°47.0039’N 146°0.1981’E RCB with center bit 2911 98.0 0.0 0.0 1200C 13°47.0724’N 146°0.1717’E Rotary drilled for casing, reentry cone 2932 266.0 0.0 0.0 1200D 13°47.0043’N 146°0.1715’E APC/XCB with center bit 2931 21.9 22.0 100.5 1200E 13°47.0043’N 146°0.1858’E APC 2911 54.4 38.1 70.0 1200F 13°47.0154’N 146°0.1860’E APC 2911 16.3 16.3 99.9 1201A 19°17.8830’N 135°5.9501’E APC 5710 1.6 1.5 93.1 1201B 19°17.8788’N 135°5.9506’E APC/XCB 5710 90.3 65.9 73.0 1201C 19°17.8829’N 135°5.9408’E APC 5710 48.1 49.5 102.9 1201D 19°17.8165’N 135°5.9519’E RCB 5709 519.6 406.8 78.3 1201E 19°17.8542’N 135°5.9491’E Rotary drilled for casing, reentry cone 5710 580.0 0.0 0.0 1202A 24°48.2449’N 122°30.0002’E APC 1274 119.5 127.14 106.4 1202B 24°48.2445’N 122°30.0077’E APC/XCB 1274 140.5 143.28 102.0 1202C 24°48.2428’N 122°30.0167’E APC/XCB 1274 97.5 100.56 105.2 1202D 24°48.2456’N 122°30.0259’E APC/XCB 1274 410.0 321.62 78.4

Note: RCB = rotary core barrel, APC = advanced hydraulic piston corer, XCB = extended core barrel.